Development and evaluation of copper-containing mesoporous bioactive glasses for bone defects therapy.

Mesoporous bioactive glasses (MBGs) are gaining increasing interest in the design of new biomaterials for bone defects treatment. An important research trend to enhance their biological behavior is the inclusion of moderate amounts of oxides with therapeutical action such as CuO. MBGs with composition (85-x)SiO2-10-CaO-5P2O5-xCuO (x = 0, 2.5 or 5 mol-%) were synthesized, investigating the influence of the CuO content and some synthesis parameters in their properties. Two series were developed; first one used HCl as catalyst and chlorides as CaO and CuO precursors, second one, used HNO3 and nitrates. MBGs of chlorides family exhibited calcium/copper phosphate nanoparticles between 10 and 20 nm in size. Nevertheless, CuO-containing MBGs of nitrates family showed metallic copper nanoparticles larger than 50 nm as well as quicker in vitro bioactive responses. Thus, MBGs of the nitrate series were coated by an apatite-like layer after 24 h soaked in simulated body fluid (SBF) a remarkably short period for a MBG containing 5% of CuO. A model, focused in the location of copper in the glass network, was proposed to relate nanostructure and in vitro behaviour. Moreover, after 24 h soaked in MEM or THB culture media, all the MBGs released therapeutic amounts of Ca2+ and Cu2+ ions. Because the quick bioactive response in SBF, the capacity to host biomolecules in their pores and to release therapeutic concentrations of Ca2+ and Cu2+ ions, MBGs of the nitrate families are proposed as excellent biomaterials for bone regeneration.

Osteogenic-angiogenic coupled response of cobalt-containing mesoporous bioactive glasses in vivo.

The incorporation of cobalt ions into the composition of bioactive glasses has emerged as a strategy of interest for bone regeneration purposes. In the present work, we have designed a set of bioactive mesoporous glasses SiO2-CaO-P2O5-CoO (Co-MBGs) with different amounts of cobalt. The physicochemical changes introduced by the Co2+ ion, the in vitro effects of Co-MBGs on preosteoblasts and endothelial cells and their in vivo behaviour using them as bone grafts in a sheep model were studied. The results show that Co2+ ions neither destroy mesoporous ordering nor inhibit in vitro bioactive behaviour, exerting a dual role as network former and modifier for CoO concentrations above 3 % mol. On the other hand, the activity of Co-MBGs on MC3T3-E1 preosteoblasts and HUVEC vascular endothelial cells is dependent on the concentration of CoO present in the glass. For low Co-MBGs concentrations (1mg/ml) cell viability is not affected, while the expression of osteogenic (ALP, RUNX2 and OC) and angiogenic (VEGF) genes is stimulated. For Co-MBGs concentration of 5 mg/ml, cell viability decreases as a function of the CoO content. In vivo studies show that the incorporation of Co2+ ions to the MBGs improves the bone regeneration activity of these materials, despite the deleterious effect that this ion has on bone-forming cells for any of the Co-MBG compositions studied. This contradictory effect is explained by the marked increase in angiogenesis that takes place inside the bone defect, leading to an angiogenesis-osteogenesis coupling that compensates for the partial decrease in osteoblast cells. STATEMENT OF SIGNIFICANCE: The development of new bone grafts implies to address the need for osteogenesis-angiogenesis coupling that allows bone regeneration with viable tissue in the long term. In this sense the incorporation of cobalt ions into the composition of bioactive glasses has emerged as a strategy of great interest in this field. Due to the potential cytotoxic effect of cobalt ions, there is an important controversy regarding the suitability of their incorporation in bone grafts. In this work, we address this controversy after the implantation of cobalt-doped mesoporous bioactive glasses in a sheep model. The incorporation of cobalt ions in bioactive glasses improves the bone regeneration ability of these bone grafts, due to enhancement of the angiogenesis-osteogenesis coupling.

Desing and comparison of bone substitutes. Study of in vivo behavior in a rabbit model. / Diseño y comparativa de biomateriales para el tratamiento de defectos óseos. Estudio de su comportamiento in vivo en modelo animal de conejo.

AIM: Compare bone formation capacity in vivo of two types of biomaterials designed as bone substitutes with respect to iliac crest autograft, one based on carbonate hydroxyapatites and the other one on bioactive mesoporous glass. MATERIALS AND METHODS: Experimental study consisting on 14 adult female New Zeland rabbits where a critical defect was made in the rabbit radius bone. The sample was divided into four groups: defect without material, with iliac crest autograft, with carbonatehydroxyapatite support, and with bioactive mesoporous glass support. Serial X-ray studies were carried out at 2, 4, 6 and 12 weeks and a microCT study at euthanasia at 6 and 12 weeks. RESULTS: In the X-ray study, autograft group showed the highest bone formation scores. Both groups of biomaterials presented bone formation similar and greater than the defect without material, but always less than in the autograft group. The results of the microCT study showed the largest bone volume in the study area in the autograft group. The groups with bone substitutes presented greater bone volume than the group without material but always less than in the autograft group. CONCLUSION: Both supports seem to promote bone formation but are not capable of reproducing the characteristics of autograft. Due to their different macroscopic characteristics, each one could be suitable for a different type of defect.

[Translated article] Design and comparison of bone substitutes. Study of in vivo behaviour in a rabbit model.

AIM: To compare the in vivo bone formation capacity of of biomaterials designed as bone substitutes with respect to iliac crest autograft, one based on carbonate hydroxiapatite and the other one on bioactive mesoporous glass. MATERIALS AND METHODS: Experimental study consisting on 14 adult female New Zeland rabbits where a critical defect was made in the rabbit radius bone. The sample was divided into four groups: defect without material, with iliac crest autograft, with carbonatehydroxyapatite scaffold, and with bioactive mesoporous glass scaffold. Serial X-ray studies were carried out at 2, 4, 6 and 12 weeks and a microCT study at euthanasia at 6 and 12 weeks. RESULTS: In the X-ray study, autograft group showed the highest bone formation scores. Both groups of biomaterials presented bone formation similar and greater than the defect without material, but always less than in the autograft group. The results of the microCT study showed the largest bone volume in the study area in the autograft group. The groups with bone substitutes presented greater bone volume than the group without material but always less than the autograft group. CONCLUSION: Both scaffolds seem to promote bone formation but are not capable of reproducing the characteristics of autograft. Due to their different macroscopic characteristics, each one could be suitable for a different type of defect.

Phytoplankton composition and abundance as indicators of aquaculture effluents impact in coastal environments of mid Gulf of California.

Composition and abundance of phytoplankton in two areas of Gulf of California, one near (ND) and one far (FD) from shrimp farms discharge, were studied in 3 seasons: late fall (farms finishing operations); spring (farms not operating); and summer (farms operating). In ND, 61 diatoms, 33 dinoflagellates, 4 cyanobacteria, and 2 silicoflagellates were identified; in FD, 72 diatoms, 38 dinoflagellates, 5 cyanobacteria, and 4 silicoflagellates were found. Thirty-three species were recorded only in ND (20 diatoms, 11 dinoflagellates, 1 silicoflagellate), whereas 39 species appeared exclusively in the FD (28 diatoms, 9 dinoflagellates, 1 cyanobacteria, 1 silicoflagellate). Thirty-seven species were common for both areas (23 diatoms, 10 dinoflagellates, 3 cyanobacteria and 1 silicoflagellate). In ND, 9 species potentially toxic (3 diatoms, 5 dinoflagellates, 1 cyanobacteria) were identified. From FD, 3 species potentially toxic (2 diatoms and 1 cyanobacteria) were found. Total abundance of phytoplankton was more than double in ND than in FD. The species richness and diversity, were greater in FD. Higher phytoplankton abundance was observed when farms were operating or finishing operations. The composition and abundance of phytoplankton is a good indicator of shrimp effluents impact, diminishing the species richness and diversity, but augmenting the abundance.

Multifunctional antibiotic- and zinc-containing mesoporous bioactive glass scaffolds to fight bone infection.

Bone regeneration is a clinical challenge which requires multiple approaches. Sometimes, it also includes the development of osteogenic and antibacterial biomaterials to treat the emergence of possible infection processes arising from surgery. This study evaluates the antibacterial properties of gelatin-coated meso-macroporous scaffolds based on the bioactive glass 80%SiO2-15%CaO-5%P2O5 (mol-%) before (BL-GE) and after being doped with 4% of ZnO (4ZN-GE) and loaded with both saturated and the minimal inhibitory concentrations of one of the antibiotics: levofloxacin (LEVO), vancomycin (VANCO), rifampicin (RIFAM) or gentamicin (GENTA). After physical-chemical characterization of materials, release studies of inorganic ions and antibiotics from the scaffolds were carried out. Moreover, molecular modelling allowed determining the electrostatic potential density maps and the hydrogen bonds of antibiotics and the glass matrix. Antibacterial in vitro studies (in planktonic, inhibition halos and biofilm destruction) with S. aureus and E. coli as bacteria models showed a synergistic effect of zinc ions and antibiotics. The effect was especially noticeable in planktonic cultures of S. aureus with 4ZN-GE scaffolds loaded with VANCO, LEVO or RIFAM and in E. coli cultures with LEVO or GENTA. Moreover, S. aureus biofilms were completely destroyed by 4ZN-GE scaffolds loaded with VANCO, LEVO or RIFAM and the E. coli biofilm total destruction was accomplished with 4ZN-GE scaffolds loaded with GENTA or LEVO. This approach could be an important step in the fight against microbial resistance and provide needed options for bone infection treatment. STATEMENT OF SIGNIFICANCE: Antibacterial capabilities of scaffolds based on mesoporous bioactive glasses before and after adding a 4% ZnO and loading with saturated and minimal inhibitory concentrations of levofloxacin, vancomycin, gentamicin or rifampicin were evaluated. Staphylococcus aureus and Escherichia coli were the infection model strains for the performed assays of inhibition zone, planktonic growth and biofilm. Good inhibition results and a synergistic effect of zinc ions released from scaffolds and antibiotics were observed. Thus, the amount of antibiotic required to inhibit the bacterial planktonic growth was substantially reduced with the ZnO inclusion in the scaffold. This study shows that the ZnO-MBG osteogenic scaffolds are multifunctional tools in bone tissue engineering because they are able to fight bacterial infections with lower antibiotic dosage.

Nucleoside deoxyribosyltransferase-II from Lactobacillus helveticus Substrate specificity studied. Pyrimidine bases as acceptors.

The nucleoside deoxyribosyltransferase (nucleoside:purine (pyrimidine) deoxyribosyltransferase, EC 2.4.2.6) fraction catalyzing specifically the transfer of the deoxyribosyl moiety from a purine (or a pyrimidine) to a pyrimidine (or a purine) exhibits a broad specificity for the acceptor base. With a pyrimidine base as the acceptor a -OH or -SH group adjacent to the N-1 atom is essential. A substituent on position 6 hinders the reaction. On positions 4 and 5 various substituent were found to influence the reaction rate and some of them give non-competent substrates. A few anomalous cases are also discussed in relation with the role of N-3. Deoxyribonucleosides can also be obtained with non-pyrimidine rings.

[Prevalence of attention deficit hyperactivity disorder in Colombian children and teenagers]. / Prevalencia del trastorno por déficit de atención-hiperactividad en niños y adolescentes colombianos.

INTRODUCTION: Attention deficit hyperactivity disorder (ADHD) is the most common neurobehavioural disorder among schoolchildren. It may persist into adulthood and affect performance in the academic, social, occupational and familial spheres, and increase the use and abuse of alcohol and psychoactive substances and the risk of having an accident. Its prevalence throughout the world varies widely and further knowledge about this situation would be valuable for the development of policies in the sector of education. AIMS: The aim of this research was to determine the prevalence of ADHD and its distribution according to subtypes in schoolchildren from Sabaneta, Antioquia, Colombia, in 2001. SUBJECTS AND METHODS: The analysis involved a cross-sectional descriptive study using a representative randomised multistage sample (which was proportional to the size of the groups) of schoolchildren between 4 and 17 years old. Measurement was performed in two stages, first by application of a screening form according to DSM IV criteria, and later a structured interview, Conners' and Intelligence tests. RESULTS: Prevalence was found to be 20.4% and 15.8% if only children with an intelligence quotient of 80 or above were considered. The combined subtype was the most frequent, with 9.6%. In public schools it was 16.2%, private 15.3%, age group from 7-11 years 16.9%, 12-17 years old 14.2%, males 20.9%, females 10.1%, low 14.7%, medium 17.4% and high socioeconomic level 10.7%, with a male to female prevalence ratio of 3.88 to 1. CONCLUSIONS: Prevalence of ADHD in the school population in a municipality in the Metropolitan Area of Medellin, Colombia, is high. The most frequent subtype was the combined type, which was predominant in males, had repercussions on academic performance and low proportions of pharmacological interventions for the disorder (15%). Programmes must be developed for the detection of this problem and subsequent intervention in the school population.

Intradiploic epidermoid cyst with intracranial hypertension syndrome: Report of two cases and literature review.

INTRODUCTION: Intradiploic epidermoid intracranial cysts (IEIC) derive from ectodermal cells and are covered with stratified squamous epithelium. They are extremely rare, and most common locations are in the occipital, frontal and parietal bones. They have a very slow growth and can be asymptomatic until becoming evident by the deformation produced. The treatment is based on the removal of the lesion, and subsequent histopathological confirmation. PRESENTATION OF CASE: Two cases are reported, with intracranial hypertension syndrome, which is very uncommon because of the slow growth of this type of pathology; however, decompensations occurring in the space-occupying lesions at intracranial level explain this type of clinical presentation. DISCUSSION: The most common presentation of intracranial intradiploic epidermoid cysts (IEIC) is asymptomatically, which is made evident by the prominence at the level of the soft tissues and then presenting less frequently local pain and cephalea; rarely the size of the lesion can cause focal neurological signs. CONCLUSION: These benign lesions, although they are of low incidence, are seen very rarely in intradiploic locations and above all, of significant size, may produce significant mass effect in patients, which was initially tolerated because of its slow growth, however, they may become decompensate and cause intracranial hypertension syndrome.

Ionophoretic and inhibitory action of the analgesic, diflunisal, on sarcoplasmic reticulum.

Diflunisal decreased the ATP-dependent transport rate and calcium accumulation by the sarcoplasmic reticulum. Inhibition of calcium transport by diflunisal was pH dependent, and a pKa of 6.7 to 6.9 was observed for the carboxylic acid group. In sealed sarcoplasmic reticulum vesicles, diflunisal at concentrations below 1 mM increased the rate of Ca2+-dependent hydrolysis of ATP; above 1 mM, the Ca2+-ATPase activity was inhibited. In purified Ca2+-ATPase, diflunisal acted only as an inhibitor. Methylation of the phenolic group of diflunisal eliminated both its analgesic and ionophoretic properties.

Mutations affecting pigmentation in man: I. Neuroectodermal melanolysosomal disease.

We describe a syndrome identified in three consanguineous families who had two and probably four common ancestors five generations ago. The syndrome is characterized by profound dysfunction of the central nervous system, silver-leaden colored hair, abnormal melanosomes and melanocytes, and abnormal inclusion bodies in fibroblasts, bone marrow histiocytes and lymphocytes which appear to represent abnormal lysosomal bodies. Because of the biochemical relationships between melanin-melanosomes and neuromelanin, we think that all the manifestations of the condition are related to and represent pleiotropic effects of a newly identified gene in man in its homozygous state. Biochemical reactions of the cells of these patients indicate presence of tyrosinase in the melanosomes.and show that the substance accumulated in cultured fibroblasts and in the bone marrow histiocytes is a PAS and Oil-red-O positive material but is Oil-red-O negative after extraction; it has the typical reactions of melanin withe the Masson and Fontana stain, but cannot be considered typical melanin, since without stain it is colorless. The ultrastructural studies showed round granules with variable matrix, similar in fibroblast and bone marrow, and with variable intensity of reaction to osmium. This mutation principally affects the neuroectoderm, but also the mesoderm.

Long distance runners and body-builders exhibit elevated plasma levels of lipoprotein(a).

A one-point cross-sectional study of 20 sedentary individuals, 20 low-aerobic athletes (body-builders), and 20 high-aerobic athletes (long distance, endurance runners) was conducted in Mexico City, Mexico to determine the influence of these diverse life-styles on the plasma levels of Lp(a). Only non-obese male subjects, aged 23-33, who were nonsmokers, non-alcoholics, and had never used anabolic steroids were included in this study. Blood samples were drawn 24 h following the last period of physical activity, and after a 12-14-h fast-period and a 15-min sitting-rest. Plasma levels of Lp(a) and other parameters, including postheparin lipoprotein lipase (LPL) and hepatic lipase (HL) activities, triglycerides (TG), total cholesterol (TC), LDL cholesterol (LDL-C), and HDL cholesterol (HDL-C), as well as % body fat and muscle mass, and maximum aerobic capacity (VO2max) were measured to determine possible correlations with Lp(a) and to serve as convenient internal standards. Mean Lp(a) concentrations were significantly higher in the runners (52 +/- 19 mg/dl) than in the body-builders (40 +/- 6.4 mg/dl, P < 0.05) and the sedentary subjects (24 +/- 5 mg/dl, P < 0.001). Positive correlations between Lp(a) and Vo2max (P < 0.001), HDL-C (P < 0.005) and HDL2-C subfraction (P < 0.005), and a negative correlation with TG were determined. Agglomerative cluster methods suggested three close-distance clusters and a fourth cluster which is composed of four runners who exhibited low LDL-C/HDL-C and high LPL/HL ratios, high mean Lp(a), HDL2-C, and Vo2max levels, but low TG levels. These data show that some individuals who maintain a life-style of very high level physical exertion may have remarkably elevated plasma Lp(a) concentrations. The highly increased concentrations of Lp(a) in high exercise athletes may represent a normal metabolic response to repeated small tissue injuries resulting from frequent and prolonged large muscle movement.

[Autism of unknown aetiology]. / El autismo de etiología desconocida.

OBJECTIVE: To review the origin, development and present state of autism, pervasive developmental disorders, progress in diagnostic tools, genetic advances, neurobiological bases, the possible causes of the increased prevalence of autism and the present treatment of the autistic condition. DEVELOPMENT: Autism is a neurobiological, life-long disorder characterized by abnormal social skills, deficient verbal and not verbal communication, symbolic and imaginative play, reasoning and related complex behaviour. Autism is 4 times more frequent in males. 70% are mentally retarded (30% mild and the rest moderate and severely retarded). Approximately 25% have convulsions and around 65% inspecific EGG abnormalities. Other conditions like ADHD, anxiety, depression may be associated. RMN: increased subarachnoidal spaces, moderate ventricular enlargement, 20% have megaloencephaly. PET and 31 PMMR show increased glucose metabolism and decreased functional links with association cortex. Mental level and language are the best prognostic indices for outcome. Pathology: reduced size of nerve cells in hippocampus, subiculum, sections of the amygdala, mamillary bodies, medial septal nucleus, decreased size of cerebellar hemispheres, posterior vermis, VI VII neocerebellar lobules. Evolution: in a small group about 9-31% live independently, 11-50% attend college. CONCLUSION: Autism is a disorder of multi-factorial origin with a genetic polygenic component and the influence of environmental elements. Treatment with risperidone improves symptoms.

[A system of multidimensional behavior assessment. A scale for parents of children from 6 to 11 years of age. Colombian version]. / Sistema de evaluación multidimensional de la conducta. Escala para padres de niños de 6 a 11 años, versión colombiana.

INTRODUCTION: Behavioral Assessment System for Children (BASC) has demonstrated to be useful in the diagnosis of Attention Deficit Disorder (ADD). PATIENTS AND METHODS: A randomized sample of 120 children, 6 to 11-year-old, participants from the school of the city of Medellín, Colombia, was selected. The sample was stratified by sex and two socioeconomic status (SES). Parents were asked to answer the BASC Parent Rating Scale (PRS) 6-11, authorized Spanish version. RESULTS: Cronbach's alpha coefficient was 0.85 for the clinical scale (9 items). It was 0.75 for the Adaptive Scale (3 items). A scale designed with 4 items to assess ADD (hyperactivity, attention problems, aggression, and conduct problems) showed an alpha coefficient of 0.82. Male children scored significantly higher than female (ANOVA, p < 0.05) in hyperactivity, conduct problems, and atypicality. Children from low SES scored significantly higher than children of high SES on the most of clinical measures (p < 0.05) and lower on the three adaptive measures. Cluster analysis selecting six clusters found a prevalence of 61.6% for normal male children. In the total sample there were a 4% at risk of DDA type II (inattentive) and 14% at risk of DDA type I (combined). CONCLUSIONS: BASC PRS (6-11) showed reliability and validity to assessing the behavior in Spanish speaking Colombian children.

Hipoglucemia grave en pacientes con diabetes mellitus 2 y azoados normales / Severe hypoglycemia in patients with diabetes mellitus type 2 and normal creatinine serum values

Resumen: ANTECEDENTES: la hipoglucemia grave es causa frecuente de hospitalización en México. OBJETIVO: identificar las características clínicas y de laboratorio asociadas con hipoglucemia grave en pacientes consecutivos con hipoglucemia grave y azoados normales. PACIENTES Y MÉTODO: estudio prospectivo en el que del 11 agosto de 2011 al 31 mayo de 2013 se incluyeron pacientes con hipoglucemia grave y creatinina normal. Se registró edad, sexo, tiempo de evolución de la diabetes mellitus, tratamiento antidiabético, comorbilidades y depuración de creatinina en orina de 24 horas. RESULTADOS: ingresaron 234 pacientes con hipoglucemia grave, 21 9% tenían creatinina normal: 13 mujeres 62% y 8 38% hombres, con edad promedio de 64.76 años límites: 42-84; 13 62% eran mayores de 60 años; 15 71% tenían más de 5 años con diabetes mellitus 2 promedio de evolución de 9.2 años; 15 recibían glibenclamida 71%, 4 en combinación con insulina 19% y 8 con metformina 38%; 2 recibían rosiglitazona más insulina. Cuatro no tenían comorbilidades 19%; 14 tenían hipertensión arterial 71% y 3 neoplasia adenocarcinoma, carcinoma gástrico y carcinoma esofágico; 11 52% ingresaron con pérdida del estado de alerta; 5 con desorientación 24%, 4 con trastornos de conducta 19%, uno con dislalia 5%; 15 de 21 71% tenían grado avanzado de deterioro renal, a pesar de tener azoados normales. CONCLUSIONES: es importante determinar la depuración de creatinina en todos los niveles de atención, única guía para prescribir tratamientos seguros de acuerdo con la función renal. La glibenclamida debe prescribirse con cautela en adultos mayores, con más de 10 años de evolución de la diabetes mellitus 2 y evitarse en los sujetos con insuficiencia renal crónica documentada.

Abstract: BACKGROUND: Severe hypoglycemia is a frequent cause of hospitalization in Mexico. OBJECTIVE: To identify the clinical and laboratory characteristics associated to severe hypoglycemia in consecutive patients with severe hypoglycemia and normal creatinine serum values. PATIENTS AND METHOD: A prospective study was done from August 11, 2011 to May 31, 2013, including patients with severe hypoglycemia and normal creatinine serum values. Age, sex, time of evolution of diabetes mellitus 2, antidiabetic treatment, comorbidities and 24-hour urine creatinine clearance were recorded. RESULTS: From 234 patients with severe hypoglycemia admitted, 21 9% had normal creatinine: 13 women 62% and 8 38% men, with a mean age of 64.76 years range: 42-84; 13 62% were older than 60 years; 15 71% had more than 5 years with DM2 mean evolution of 9.2 years; 15 received glibenclamide 71%, 4 in combination with insulin 19% and 8 with metformin 38%. Two received rosiglitazone plus insulin. Four patients had not comorbidities 19%; 16 had arterial hypertension 71% and 3, neoplasms adenocarcinoma, gastric carcinoma and esophageal carcinoma. Eleven patients 52% were admitted with syncope, 5 with disorientation 24%, 4 with conduct disorders 19% and one with dyslalia 5%; 15 of 21 patients 71% had advanced degrees of renal impairment, despite normal creatinine serum values. CONCLUSIONS: It is important to perform creatinine clearance at all levels of care, the only guide for safe treatments according to kidney function. Glibenclamide should be cautiously prescribed in older adults with a history of more than 10 years of diabetes mellitus 2 and should be avoided in those with documented chronic renal failure.

Cooperative effects of Ca2+ and Sr2+ on sarcoplasmic reticulum adenosine triphosphatase.

The intrinsic fluorescence of purified Ca-ATPase from skeletal sarcoplasmic reticulum was measured in the presence of various concentrations of Ca2+, Sr2+, and Ba2+. Ca2+ and Sr2+ induce positive cooperative fluorescence enhancement, whereas Ba2+ does not change the fluorescence of ATPase. ATP does not seem to modify the kinetic parameters of Ca2+ and Sr2+ binding to ATPase. Nevertheless, p-nitrophenylphosphate hydrolysis, activated by Ca2+ or Sr2+ at various pHs, changes the affinity and the cooperative behavior for both cations and two components appear in the Hill plots. For Ca2+, nH of 1.6 to 3.5 were obtained, and 1.06 to 1.83 for Sr2+; nH changes of the second component seem to be pH dependent. Differences in the ratio between rates of Ca2+ transport and substrate hydrolysis by sarcoplasmic reticulum were found, i.e., two for ATP and one for p-nitrophenylphosphate. For Sr2+ this ratio was one for either ATP or p-nitrophenylphosphate.

Trans-N-deoxyribosylase: purification by affinity chromatography and characterization.

trans-N-Deoxyribosylase (EC 2.4.2.6) is usually considered as a single protein catalyzing indifferently the transfer of the deoxyribosyl moiety to and from a purine or a pyrimidine base. Affinity chromatography of an extract from Lactobacillus helveticus with two types of ligands allowed the separation and purification of two distinct trans-N-deoxyribosylases. One catalyzes specifically the deoxyribosyl transfer to and from purine bases exclusively: trans-N-deoxyribosylase-I, the other catalyzes the transfer to and from pyrimidine and purine bases: trans-N-deoxyribosylase-II. A Tris inhibition study showed a markedly different susceptibility of the two enzymes. Preliminary results indicate that the purine-specific enzyme is a polymeric enzyme of molecular weight 86 000 (+/- 4000).

Trans-N-deoxyribosylase: substrate specificity studies. Purine bases as acceptors.

A series of purine bases and analogues were tested as substrates for trans-N-deoxyribosylase (EC 2.4.2.6). It was observed that the pyrimidine ring and its substituents on positions 1, 2 and 6, are of minor importance. On the other hand only a few modifications are tolerated on the imidazole moiety, as follows. 1. A tautomeric proton must be present on the imidazole ring. The "usual" shift is between position 9 and 7. 2. The position of the tautomeric proton governs the site of substitution. 3. For steric reasons no substituent is allowed on position 8.

Mitochondrial calcium release as induced by Hg2+.

Addition of Hg2+ to mitochondria of rat kidney induces efflux of intramitochondrial Ca2+. This reaction is accompanied by a diminution of the NAD(P)H/NAD(P) ratio and a decrease of the internal negative membrane potential. These effects were enhanced by dithiothreitol. The binding of mercuric ions to mitochondria saturates with a maximal binding of 9 nmol min-1 mg-1. The stoichiometry between Ca2+ released and Hg2+ bound showed that in the presence of dithiothreitol, the binding of approximately 1 nmol of Hg2+/mg of protein suffices to induce the release of the accumulated Ca2+. In the electrophoretic analysis of Hg-labeled mitochondrial proteins it was found that 203Hg2+ bound mainly to proteins that have molecular masses of 20 and 30 kDa. It is proposed that Hg2+-induced Ca2+ release is due to modification of--SH groups of these latter proteins.