Circulating miR-30b-5p levels in plasma as a novel potential biomarker for early detection of breast cancer.

BACKGROUND: Recently, microRNAs have been demonstrated to be potential non-invasive biomarkers for diagnosis, prognosis assessment or prediction of response to treatment in cancer. In this study, we evaluate the potential of miR-30b-5p as a biomarker for early diagnosis of breast cancer (BC) in tissue and plasma. METHODS: Expression of miR-30b-5p was determined in a series of 112 BC and 40 normal breast tissues. Circulating miR-30b-5p levels in plasma samples were determined in a discovery cohort of 38 BC patients and 40 healthy donors and in a validation cohort of 83 BC patients and 83 healthy volunteers. miR-30b-5p expression was measured by quantitative real-time PCR and receiver operating characteristics curve analysis was carried out. RESULTS: The miR-30b-5p expression was significantly lower in BC tissue than in healthy breast samples. In contrast, circulating miR-30b-5p levels were significantly higher in BC patients compared with healthy donors. Furthermore, circulating miR-30b-5p levels were significantly higher in patients with positive axillary lymph node and de novo metastatic patients. Receiver operating characteristics curve analysis demonstrated a good diagnostic potential of miR-30b-5p to detect BC even at an early stage of the disease. CONCLUSION: Thus, we highlight the potential of miR-30b-5p as a non-invasive, fast, reproducible and cost-effective diagnostic biomarker of BC.

Brote masivo de intoxicación por monóxido de carbono en los telespectadores de un partido de fútbol / Mass carbon monoxide poisoning among television viewers of a football match

Introducción. El objetivo fue estudiar un brote de intoxicación por monóxido de carbono (CO) y las características de los casos asintomáticos. Métodos. El 2 de febrero de 2015 un grupo de más de 30 telespectadores de un partido de fútbol contactó con el servicio de urgencias por una supuesta intoxicación por CO procedente de una estufa de butano. Se realizó una inspección ocular del local de la exposición y un estudio epidemiológico descriptivo. Según el tipo de variables, la existencia de una asociación estadística se estudió con la prueba exacta de Fisher o el test de Kruskal-Wallis. Resultados. Se vieron afectados 34 de 39 sujetos (87,2%). Los expuestos tenían una media de edad de 43,8años (DE=22,1) y el 28,2% (11/39) eran mujeres. El tiempo de exposición fue de 52,4min (DE=21,0) y la distancia a la estufa de 4,2m (DE=2,5). Los síntomas más frecuentes fueron cefalea (50%), náuseas (20,6%), pérdida de fuerza (20,6%) y vértigo (14,7%). Los niveles de carboxihemoglobina (COHb) fueron muy elevados (13,8%±5,8). El 97,1% precisó oxigenoterapia y el 39,4% tratamiento en cámara hiperbárica. Un 29,5% de los casos no presentaron síntomas, y respecto a los casos sintomáticos, estos mostraron niveles similares de COHb (13,6% vs. 15,3%, diferencia no significativa), pero un tiempo de exposición inferior (38,3min vs. 53,3min; p<0,036). Conclusiones. Casi una tercera parte de las personas expuestas fueron asintomáticas aun con niveles de COHb similares a los casos sintomáticos, e incluso la mayoría precisaron tratamiento con oxígeno en cámara hiperbárica (AU)

Background. The objective was to study a mass carbon monoxide (CO) poisoning and the characteristics of the asymptomatic cases. Methods. On the 2nd of February, 2015, a group of more than 30 television viewers of a football match contacted the emergency department due to suspected CO poisoning from a butane stove. A visual inspection of the location of the exposure and a descriptive epidemiological study were conducted. Based on the type of variable, the presence of a statistical association was studied with Fisher's exact test or the Kruskal-Wallis test. Results. Thirty-four of the 39 individuals were affected (87.2%). The exposed individuals had a mean age of 43.8 years (SD, 22.1), and 28.2% (11/39) were women. The time of exposure was 52.4min (SD, 21.0), and the mean distance from the oven was 4.2m (SD, 2.5). The most common symptoms were headache (50%), nausea (20.6%), weakness (20.6%) and dizziness (14.7%). The carboxyhaemoglobin (COHb) levels were very high (13.8% ±5.8%). Some 97.1% of the individuals required oxygen therapy, and 39.4% required hyperbaric chamber treatment. Some 29.5% of the cases had no symptoms but showed COHb levels similar to those that did have symptoms (13.6% vs. 15.3%, nonsignificant difference). The asymptomatic cases had a shorter exposure time (38.3min vs. 53.3min; P<.036). Conclusions. Almost a third of the exposed individuals were asymptomatic, even with COHb levels similar to those of the symptomatic patients, and the majority of these asymptomatic patients even required oxygen treatment in a hyperbaric chamber (AU)

Mass carbon monoxide poisoning among television viewers of a football match. / Brote masivo de intoxicación por monóxido de carbono en los telespectadores de un partido de fútbol.

BACKGROUND: The objective was to study a mass carbon monoxide (CO) poisoning and the characteristics of the asymptomatic cases. METHODS: On the 2nd of February, 2015, a group of more than 30 television viewers of a football match contacted the emergency department due to suspected CO poisoning from a butane stove. A visual inspection of the location of the exposure and a descriptive epidemiological study were conducted. Based on the type of variable, the presence of a statistical association was studied with Fisher's exact test or the Kruskal-Wallis test. RESULTS: Thirty-four of the 39 individuals were affected (87.2%). The exposed individuals had a mean age of 43.8 years (SD, 22.1), and 28.2% (11/39) were women. The time of exposure was 52.4min (SD, 21.0), and the mean distance from the oven was 4.2m (SD, 2.5). The most common symptoms were headache (50%), nausea (20.6%), weakness (20.6%) and dizziness (14.7%). The carboxyhaemoglobin (COHb) levels were very high (13.8% ±5.8%). Some 97.1% of the individuals required oxygen therapy, and 39.4% required hyperbaric chamber treatment. Some 29.5% of the cases had no symptoms but showed COHb levels similar to those that did have symptoms (13.6% vs. 15.3%, nonsignificant difference). The asymptomatic cases had a shorter exposure time (38.3min vs. 53.3min; P<.036). CONCLUSIONS: Almost a third of the exposed individuals were asymptomatic, even with COHb levels similar to those of the symptomatic patients, and the majority of these asymptomatic patients even required oxygen treatment in a hyperbaric chamber.

Factores de riesgo asociados a pacientes tuberculosos con microscopía del esputo positiva / Risk factors associated to tuberculosis patients with positive sputum microscopy

Objetivo: El factor determinante para la producción de casos de tuberculosis por transmisión exógena es la existencia de pacientes con baciloscopias positivas. El objetivo de este estudio fue determinar los factores de riesgo asociados a pacientes con microscopía positiva en secreciones respiratorias. Métodos: Se estudiaron los casos incidentes de tuberculosis del período 1992-1998 en la provincia de Lleida. Las variables del estudio fueron: edad, sexo, infección por el VIH, uso de drogas por vía parenteral (UDVP), consumo de alcohol, existencia de cavernas y resultado de la microcopia del esputo. Se calculó la tasa de incidencia por 100.000 personas-año. La asociación de la variable dependiente -caso de tuberculosis con baciloscopia positiva- con el resto de variables independientes se determinó con la odds ratio (ORc, cruda, y ORa, ajustada mediante regresión logística no condicional) con su intervalo de confianza (IC) del 95 por ciento. Resultados: Se detectaron 905 casos nuevos de tuberculosis. La tasa de incidencia del período 1992-1998 decreció desde 38,8 a 30,8. El 44,9 por ciento de los casos (n = 406) presentó una baciloscopia positiva. El riesgo de ser bacilífero se asoció positivamente con la presencia de cavernas en la radiografía de tórax (ORa = 6,8; IC del 95 por ciento, 4,8-9,5), el género masculino (ORa = 1,8; IC del 95 por ciento, 1,3-2,6) y el consumo de alcohol (ORa = 1,6; IC del 95 por ciento, 1,1-2,3) y fue inferior en los menores de 15 años (ORa = 0,2; IC del 95 por ciento, 0,1-0,5) y coinfectados por el VIH (ORa = 0,5; IC del 95 por ciento, 0,3-0,9). Conclusiones: La infección por el VIH implica un reducido impacto en la endemia tuberculosa. El estudio de contactos y la implantación de tratamientos directamente observados se deben considerar no sólo para los coinfectados por el VIH y UDVP, sino para adultos varones, con consumo excesivo de alcohol, especialmente si presentan lesiones cavernosas (AU)

[Risk factors associated to tuberculosis patients with positive sputum microscopy]. / Factores de riesgo asociados a pacientes tuberculosos con microscopía del esputo positiva.

OBJECTIVE: The main factor responsible for producing new cases of tuberculosis by exogen transmission is the existence of Mycobacterium tuberculosis in the sputum of tuberculosis patients. The objective of this study was to determine the risk factors associated to positive smear tuberculosis cases in Lleida (Spain). METHODS: We studied new cases of tuberculosis over the period 1992-1998. The variables considered were: age, gender, coinfection with HIV, injection drug use (IDU), consumption of alcohol, existence of caverns in thorax X-ray, and laboratory results of direct smear examination. We calculated the incidence rates for 100,000 persons-year. The association between the dependent variable case of tuberculosis with positive Mycobacterium tuberculosis smear and the remaining independent variables were assessed obtaining odds ratios (OR) and 95% confidence intervals (CI) (crude cOR and adjusted aOR by non conditional logistic regression). RESULTS: We detected 905 new cases of tuberculosis. The rates in the period 1992-1998 decreased from 38.8 to 30.8. 44.9% of cases (n = 406) presented a positive direct smear. There was a positive association between the risk of being a positive smear patient and having caverns in thorax x-ray (aOR = 6.8; 95% CI, 4.8-95), being male (aOR = 1.8; 95% CI, 1.3-2.6) and consuming alcohol (aOR = 1.6; 95% CI,1.1-2.3) and this risk was significant lower in those under 15 years old (aOR = 0.2; 95% CI, 0.1-0.5), and coinfection with HIV (aOR = 0.5; 95% CI, 0.3-0.9). CONCLUSIONS: HIV infection implies a reduced impact in endemecity of tuberculosis. Study of contacts and the implementation of directly observed treatment must be considered not only for coinfected HIV cases and IDU but also for adult males, especially those who consume alcohol, particularly when they have caverns.

[Food poisoning outbreak due to the consumption of spaghetti a la carbonara caused by Salmonella enteritidis]. / Brote de toxiinfección alimentaria por consumo de espaguetis a la carbonara causado por Salmonella enteritidis.

INTRODUCTION: This paper reports a clinico-epidemiological and microbiological investigation conducted into an outbreak of gastrointestinal infection due to Salmonella enteritidis, where the most likely food vehicle was spaghetti a la carbonara. METHODS: An historic cohort study was conducted out among persons exposed to menus at a school canteen. Data were gathered on age, sex, foods consumed and clinical symptoms. School premises and menus were inspected, food samples obtained (spaghetti and meat balls), and stool samples taken from 30 affected subjects and 8 food handlers. Isolated strains were studied using pulsed-field electrophoresis. Attack rates were computed, and the odds ratio adjusted for the remaining foodstuffs (ORa) used to calculate the independent contribution made by the respective foods to risk of infection. RESULTS: Study coverage was 75.7% (140/185). The overall attack rate was 72.1% (101/140), with 12.9% of those affected requiring hospitalisation. The multivariate analysis showed that, while the spaghetti maintained its association (ORa = 8.4; 95% CI 1.4-51.8), the meat balls registered a reduction in risk (ORa = 1.8; 95% CI 0.4-7.5). S. enteritidis was isolated in stool cultures from 28 affected subjects, and in 2 blood and 6 stool cultures from food handlers (5 of whom were classed as cases). Moreover, S. enteritidis was also isolated in the food samples. On pulsed-field electrophoresis, the strains registered the same electrophoresis pattern. CONCLUSIONS: This outbreak serves to underscore the gravity of Salmonella spp. food poisoning, the danger of using inadequately cooked eggs, and the importance of interviewing food handlers to ensure proper classification (i.e., as patients or carriers). Existing recommendations as to the use of pasteurised egg products ought to be extended in scope.

Primary Sjögren's syndrome in men: clinical and immunological characteristics.

OBJECTIVE: To determine the clinical and immunological characteristics of primary Sjögren's syndrome (SS) in men from a large series of unselected patients with this condition. METHODS: We studied 223 consecutive patients (204 women and 19 men; mean age at onset 53 y, range 15-87 y, mean disease duration 77 months) with primary SS visited in our units. All these patients fulfilled 4 or more of the diagnostic criteria for SS proposed by the European Community Study Group in 1993. RESULTS: Nineteen (9%) patients were men and they represent the male group described in this paper. Extraglandular manifestations during the course of their disease were present in 10 (53%) of our male patients with primary SS: articular involvement in 4 (21%) patients, interstitial pneumopathy in 3 (16%) and peripheral neuropathy in 2 (11%). ANA were positive in 13 (68%) patients, RF in 5 (31%), anti-Ro/SS-A in 3 (16%) and cryoglobulins in 1/14 (7%). When compared with women, men with primary SS presented a lower prevalence of articular involvement (21 percent; vs 46%, P=0.03, OR 0.32, CI 0.07-0.97). CONCLUSION: Although primary SS is typically a disease of middle-aged women, clinicians should note that it may be diagnosed in male patients. Except for a lower prevalence of articular involvement, we could no find any notable differences in clinical and immunological characteristics between male and female patients with primary SS.

[Validity of the notifications of red measles based on clinical diagnosis in Cataluna, Spain]. / Validez de las notificaciones de sarampión basadas en el diagnóstico clínico en Cataluña.

OBJECTIVE: To compare the characteristics of clinical cases of measles with confirmed cases of measles registered in Cataluña during a period of four months. PATIENTS AND METHODS: An epidemiological survey was carried out on 171 cases of measles detected by a specific system of surveillance. The survey included data on age, sex, clinical symptoms, laboratory confirmation, immunization status and probable site of transmission. The relationship between the variable case (with or without laboratory confirmation) and the rest of variables was determined by the adjusted odds ratio, using a model of logistic regression. RESULTS: The epidemiological survey showed that 30.4% (52/171) had laboratory confirmation, 12.9% (22/171) had epidemiological confirmation and the rest, 56.7% (97/171) only complied with the clinical definition. The rash had a longer duration in confirmed cases (5.9 days) than in non confirmed cases (5.2 days). The lack of laboratory confirmation was associated with age younger than 5 years (ORa = 0.1; 95% CI 0.1-0.8), but there were no differences in sex, immunization status or others clinical symptoms. CONCLUSION: In clinical cases of measles the duration of the rash was lower than confirmed cases. The proportion of cases with laboratory confirmation was low (30.4%) and should be increased in the future. History of previous immunization ought not to rule out diagnosis of measles.

Divergent Hsc70 binding properties of mitochondrial and cytosolic aspartate aminotransferase. Implications for their segregation to different cellular compartments.

Cytosolic Hsc70 discriminates between the homologous mitochondrial and cytosolic isozymes of aspartate aminotransferase, binding exclusively the mitochondrial form. By screening a library of synthetic peptides spanning the sequence of the mitochondrial enzyme, we have identified binding sites in this polypeptide that interact with Hsc70. These potential binding sites are scattered over the entire sequence and map to secondary structure elements, particularly the alpha-helix, that are partly exposed on the surface of the native protein. Several peptides corresponding to analogous positions in the cytosolic enzyme sequence do not bind to Hsc70. Phylogenetic analyses suggest that Hsc70 binding sequences have diverged as a consequence of biochemical specialization ensuring differential interaction of each isozyme with the cellular machinery in charge of protein folding and translocation.

Insight into the conformation of protein folding intermediate(s) trapped by GroEL.

Many aspects of the mechanism by which the GroEL/ES chaperonins mediate protein folding are still unclear, including the amount of structure present in the substrate bound to GroEL. To address this issue we have analyzed the susceptibility to limited proteolysis and to alkylation of cysteine residues of mitochondrial aspartate aminotransferase (mAAT) bound to GroEL. Several regions of the N-terminal portion of GroEL-bound mAAT are highly susceptible to proteolysis, whereas a large core of about 200 residues containing the C-terminal half of the polypeptide chain is protected in the complex. This protection does not extend to the mAAT sulfhydryl groups which in the GroEL-mAAT complex have similar reactivity as in fully unfolded mAAT. These results suggest that the mAAT species bound to GroEL represent folding intermediates with a conformation that is substantially more disorganized than that of the native state. The N-terminal half of the molecule is more flexible and lies exposed at the mouth of the central cavity of GroEL. The more compact C-terminal section of mAAT, which contains residues located at the subunit interface in the native dimer, appears to be hidden in the central cavity of GroEL. Thus, the bulk of the interactions in the GroEL.mAAT complex seems to involve residues from the more compact C-terminal section of the substrate.

Opposite behavior of two isozymes when refolding in the presence of non-ionic detergents.

GroEL has a greater affinity for the mitochondrial isozyme (mAAT) of aspartate aminotransferase than for its cytosolic counterpart (cAAT) (Mattingly JR Jr, Iriarte A, Martinez-Carrion M, 1995, J Biol Chem 270:1138-1148), two proteins that share a high degree of sequence similarity and an almost identical spatial structure. The effect of detergents on the refolding of these large, dimeric isozymes parallels this difference in behavior. The presence of non-ionic detergents such as Triton X-100 or lubrol at concentrations above their critical micelle concentration (CMC) interferes with reactivation of mAAT unfolded in guanidinium chloride but increases the yield of cAAT refolding at low temperatures. The inhibitory effect of detergents on the reactivation of mAAT decreases progressively as the addition of detergents is delayed after starting the refolding reaction. The rate of disappearance of the species with affinity for binding detergents coincides with the slowest of the two rate-limiting steps detected in the refolding pathway of mAAT. Limited proteolysis studies indicate that the overall structure of the detergent-bound mAAT resembles that of the protein in a complex with GroEL. The mAAT folding intermediates trapped in the presence of detergents can resume reactivation either upon dilution of the detergent below its CMC or by adding beta-cyclodextrin. Thus, isolation of otherwise transient productive folding intermediates for further characterization is possible through the use of detergents.

Refolding intermediates of acid-unfolded mitochondrial aspartate aminotransferase bind to hsp70.

The cytosolic (cAAT) and mitochondrial (mAAT) isozymes of eukaryotic aspartate aminotransferase share a high degree of sequence identity and almost identical three-dimensional structure. The rat liver proteins can be refolded and reassembled into active dimers after unfolding at low pH. However, refolding of the mitochondrial form after unfolding at pH 2.0 is arrested in the presence of hsp70, whereas this chaperone does not affect the refolding of the cytosolic isozyme unfolded under similar conditions. To elucidate the nature of the differential interaction between hsp70 and the two transaminase forms, we have characterized their refolding from their acid-unfolded states. The recovery of activity of the cytosolic enzyme is monophasic and can be adequately described by a single first-order reaction. By contrast, two sequential first-order rate-limiting steps can be detected for the refolding and reactivation of the mitochondrial protein. The overall refolding pathway of mAAT includes a very fast collapse to an intermediate with 80% of the secondary structure of the active dimer. This is followed by a slow isomerization to form assembly-competent monomers that rapidly associate to form an inactive dimer and a final structural rearrangement of the dimer to the native conformation. Analysis of the interaction of hsp70 with intermediates along the folding pathway of mAAT shows that the polypeptide loses its ability to bind to the chaperone after it has proceeded through the first isomerization/fast dimerization steps. Thus it appears that only the first collapsed intermediate states in the folding of mAAT bind hsp70. By contrast a faster refolding of cAAT from this collapsed state could explain, at least in part, the inability of hsp70 to bind this isozyme.

[Fever of unknown origin in patients with HIV infection]. / Fiebre de origen desconocido en pacientes con infección por el HIV.

BACKGROUND: The aim of the study was to describe the etiology and clinical characteristics of fever of uncertain origin (FUO) among HIV-infected patients. METHODS: Prospective analysis of 35 episodes of FUO in HIV-infected patients from Balearic Islands that were studied through established guidelines. RESULTS: Most patients were at advanced stages of HIV-1 infection (mean CD4 cell count, 60/mm3). Mean duration of fever until diagnosis was 57 days. Average time of hospitalization until etiological diagnosis of FUO was 26 days (range: 8-127 days). The cause of FUO was identified in 33 cases (94%). Tuberculosis accounted for 18 cases (51%) and visceral leishmaniasis for 8 cases (23%). Other opportunistic infections were the cause of FUO in 8 cases (17%). In one patient, fever was due to Kaposi's sarcoma. Two patients died while febrile, without and identified etiology. Four patients had more than one cause that could contribute to FUO. Imaging techniques that yielded more diagnostic information were abdominal ultrasonography and serial chest X-ray. Leishmania serology and tuberculin skin test showed a high specificity but low sensitivities. Invasive procedures with a highest diagnostic field were fine needle aspirate of lymph nodes, and liver biopsy. CONCLUSIONS: FUO is more frequent in advanced stages of HIV disease. In our area, FUO is caused primarily by endemic opportunistic infections specially TB and visceral leishmaniasis, and rarely can be attributable to HIV or neoplastic diseases.

Conformational analyses on soluble and surface bound osteopontin.

Immunohistology of calvarial sections revealed that staining with monoclonal anti-osteopontin antibodies (clone MPIIIB10) is minimal unless sections are first treated with EDTA. In contrast, following treatment of sections with EDTA, strong staining of mineralizing osteoid areas and osteoblast-like cells was noted (Fig. 1B). Immunostaining for osteopontin appeared to be specific in that controls which substituted rabbit IgG or normal mouse ascites fluid for monoclonal antibody, or which omitted monoclonal antibody uniformly gave background results (Fig. 1C). In an effort to circumvent problems of antibody accessibility we examined the immunoreactivity of OP when adsorbed to plastic and hydroxyapatite surfaces. Although OP bound to plastic surfaces is reactive with MPIIIB10 antibodies, OP adsorbed to hydroxyapatite crystal surfaces is not recognized by these antibodies as assessed by two detection methods. These results demonstrate that most or all of OP bound to hydroxyapatite exhibits a different conformation than when bound to plastic surfaces. On the basis of immunohistologic results with calvarial sections, we suggest that the conformation of native OP in bone and of isolated OP adsorbed to hydroxyapatite may be similar. Finally, solution circular dichroism and Fourier-transformed infrared spectroscopic studies indicate that the conformation of bone OP is dependent upon its concentration, and, secondarily to the presence or absence of calcium ion. With both spectroscopic methods, addition of calcium appeared to increase the extent of disordered structure. We suggest that these findings support our hypothesis that bone matrix proteins exhibit a different conformation when adsorbed on hydroxyapatite crystal surfaces. Assumption of a more organized secondary structure in concentrated OP solutions (i.e., 15 mg/ml) is consistent with these results in that local concentrations of OP within a semisolid matrix may approach or exceed levels used here.

Acid-induced reversible unfolding of mitochondrial aspartate aminotransferase.

The acid-induced reversible unfolding of several forms of the mitochondrial isoenzyme of mammalian aspartate aminotransferase, including its precursor form, has been characterized under equilibrium conditions. A minimum of two transitions can be detected for the holoenzyme (pyridoxal form). One transition takes place at pH 3.6 and corresponds to the monomerization of the dimeric protein. The second transition is centered at pH 3.3 and represents the disappearance of much of the tertiary and secondary structures. The presequence peptide in the precursor protein does not affect the equilibria nor the rate of unfolding in the pH range from 7.5 to 2.0. The presence of the cofactor, pyridoxal 5'-phosphate, stabilizes the protein against acid denaturation. At pH 2.0, the protein retains significant amounts of secondary structure (26% alpha-helix, 20% beta-structure). Increasing the ionic strength at pH 2.0 results in significant changes in the secondary structure of the unfolded protein that acquires some of the characteristics ascribed to a compact molten globule. According to the circular dichroism spectra these changes are characterized by an increase in beta-structure, although Fourier transform infrared spectroscopy analysis indicates that this increase in beta-structure is due mostly to the formation of intermolecular beta-sheet as a consequence of protein aggregation. The formation of high molecular weight aggregates has been confirmed by analytical ultracentrifugation. Following neutralization of the acid-unfolded state at low ionic strength both mature and precursor proteins refold to their native active state (> 80% yield). By contrast the compact state present at pH 2.0 and high ionic strength is unable to recover its activity following neutralization. Thus, this compact state does not appear to represent an intermediate in the folding pathway of the protein, but rather a dead end product of aggregation, which may reflect the intrinsic tendencies of the unfolded protein to oligomerize at intracellular salt concentrations unless controlled by factors such as chaperones present in the cellular environment.

Cytosolic serine hydroxymethyltransferase. Deamidation of asparaginyl residues and degradation in Xenopus laevis oocytes.

Rabbit liver cytosolic serine hydroxymethyltransferase exists as a set of subforms which exhibit different isoelectric points. Previous studies have shown that deamidation of an asparagine residue at position 5 of the amino acid sequence accounted for some of the charge heterogeneity (Artigues, A., Birkett, A., and Schirch, V. (1990) J. Biol. Chem. 265, 4853-4858). The present study has also identified asparagine 220 as being partially deamidated. An estimated 25-30% of the purified enzyme contains an isoaspartyl residue at position 220. This suggests that deamidation of asparagine 220 occurs by the beta-aspartyl shift mechanism. Western blot analysis of purified cytosolic serine hydroxymethyltransferase, after isoelectric focusing under reducing and denaturing conditions, showed four subforms of the individual subunits with respect to isoelectric point. Extracts from 3-day- and 3.5-year-old rabbit livers showed the presence of these same four subunit subforms. Purified cytosolic serine hydroxymethyltransferase was found to be degraded in 24 h after mechanical injection into Xenopus laevis oocytes. However, when the first 14 amino acid residues are removed from the enzyme by digestion with chymotrypsin, leaving a fully catalytically active enzyme, the rate and extent of degradation of the truncated enzyme in oocytes were significantly reduced. One of the deamidated asparagine residues is at position 5, suggesting that this deamidation site may be a signal for degradation of the enzyme.