Protein tyrosine phosphatases: a diverse family of intracellular and transmembrane enzymes.

Protein tyrosine phosphatases (PTPs) represent a diverse family of enzymes that exist as integral membrane and nonreceptor forms. The PTPs, with specific activities in vitro 10 to 1000 times greater than those of the protein tyrosine kinases would be expected to effectively control the amount of phosphotyrosine in the cell. They dephosphorylate tyrosyl residues in vivo and take part in signal transduction and cell cycle regulation. Most of the transmembrane forms, such as the leukocyte common antigen (CD45), contain two conserved intracellular catalytic domains; but their external segments are highly variable. The structural features of the transmembrane forms suggest that these receptor-linked PTPs are capable of transducing external signals; however, the ligands remain unidentified. A hypothesis is proposed explaining how phosphatases might act synergistically with the kinases to elicit a full physiological response, without regard to the state of phosphorylation of the target proteins.

A calcium-dependent protein kinase with a regulatory domain similar to calmodulin.

Calcium can function as a second messenger through stimulation of calcium-dependent protein kinases. A protein kinase that requires calcium but not calmodulin or phospholipids for activity has been purified from soybean. The kinase itself binds calcium with high affinity. A complementary DNA clone for this kinase has been identified; it encodes a protein with a predicted molecular mass of 57,175 daltons. This protein contains a catalytic domain similar to that of calmodulin-dependent kinases and a calmodulin-like region with four calcium binding domains (EF hands). The predicted structure of this kinase explains its direct regulation via calcium binding and establishes it as a prototype for a new family of calcium-regulated protein kinases.

Primary structure and functional expression of the beta 1 subunit of the rat brain sodium channel.

Voltage-sensitive sodium channels are responsible for the initiation and propagation of the action potential and therefore are important for neuronal excitability. Complementary DNA clones encoding the beta 1 subunit of the rat brain sodium channel were isolated by a combination of polymerase chain reaction and library screening techniques. The deduced primary structure indicates that the beta 1 subunit is a 22,851-dalton protein that contains a single putative transmembrane domain and four potential extracellular N-linked glycosylation sites, consistent with biochemical data. Northern blot analysis reveals a 1,400-nucleotide messenger RNA in rat brain, heart, skeletal muscle, and spinal cord. Coexpression of beta 1 subunits with alpha subunits increases the size of the peak sodium current, accelerates its inactivation, and shifts the voltage dependence of inactivation to more negative membrane potentials. These results indicate that the beta 1 subunit is crucial in the assembly, expression, and functional modulation of the heterotrimeric complex of the rat brain sodium channel.

Protein tyrosine dephosphorylation and signal transduction.

The protein tyrosine phosphatases comprise a family of enzymes that specifically dephosphorylate tyrosyl residues. Determination of the amino acid sequence of a major low molecular mass form isolated from human placenta (PTPase 1B) provided the basis for the first identification of transmembrane proteins that bear intracellular phosphatase domains. The existence of such molecules, bearing the hallmarks of receptors, raises the exciting possibility of a novel mechanism of signal transduction in which the early events involve the ligand-induced dephosphorylation of tyrosyl residues in proteins.

Osteogenesis imperfecta. The position of substitution for glycine by cysteine in the triple helical domain of the pro alpha 1(I) chains of type I collagen determines the clinical phenotype.

Skin fibroblasts grown from three individuals with osteogenesis imperfecta (OI) each synthesized a population of normal type I collagen molecules and additional molecules that had one or two alpha 1(I) chains that contained a cysteine residue within the triple-helical domain, a region from which cysteine normally is excluded. The patients had very different phenotypes. One patient with OI type I had a population of alpha 1(I) chains in which glycine at position 94 of the triple helix was substituted by cysteine; a patient with OI type III had a population of alpha 1(I) chains in which glycine at position 526 of the triple helix was substituted by cysteine; and the third patient, with OI type II, had a cysteine for glycine substitution at position 718 of the alpha 1(I) chain. From all three patients, molecules that contained two mutant chains formed interchain, intramolecular disulfide bonds, and although less stable to thermal denaturation than normal molecules, they were more stable than molecules that contained only a single mutant chain. These findings indicate that substitutions for glycine within the triple-helical domain of the alpha 1(I) chain are not invariably lethal and that their phenotypic effect largely depends on the nature of the substituting residue and its location in the chain.

Plant and fungal calmodulin: Ca2+-dependent regulation of plant NAD kinase.

Although little is known about the role(s) of second messengers, including free Ca2+, in plant cells there has been increasing evidence for a role for Ca2+ in metabolic regulation in plants. The recent demonstration that the Ca2+-binding protein, calmodulin exists in extracts of higher plants and basidiomycete fungi provides a basis for understanding Ca2+-dependent metabolic regulation in plant cells. In this review we summarize the similarities and differences of plant, fungal and mammalian calmodulin. We also discuss the known in vitro functions of calmodulin in higher plants. A Ca2+-calmodulin-dependent NAD kinase has been purified to homogeneity from extracts of pea seedlings and shown to be absolutely dependent upon calmodulin and microM levels of free Ca2+ for activity. The available evidence suggest that this Ca2+-calmodulin-dependent NAD kinase is the major form of plant NAD kinase and that this regulatory enzyme is localized in the chloroplast. A model is presented which predicts that the rate of photosynthesis is regulated by a receptor-mediated change in the level of chloroplastic free Ca2+ upon illumination. Free Ca2+, acting as a second messenger, forms a Ca2+-calmodulin complex thus converting calmodulin to its active conformation. This Ca2+-calmodulin complex then activates chloroplastic NAD kinase resulting in an increased NADP/NAD ratio.

Amino acid sequence of the Ca2(+)-triggered luciferin binding protein of Renilla reniformis.

The complete amino acid sequence of the Ca2(+)-triggered luciferin binding protein (LBP) of Renilla reniformis has been determined. The apoprotein has an unblocked amino terminus and contains 184 residues with a calculated Mr of 20,541. LBP is a member of the EF-hand superfamily of Ca2(+)-binding proteins and bears three predicted EF-hand domains. The sequence and organization of EF-hand domains are similar to those of the Ca2(+)-dependent photoprotein, aequorin.

Purification of calmodulin-stimulated cyclic nucleotide phosphodiesterase by monoclonal antibody affinity chromatography.

Immobilized ACC-1 and ACAP-1 antibodies are effective tools for the purification of active calmodulin-dependent phosphodiesterases. ACC-1 antibody binds all bovine and rat brain isozymes in a Ca2+-dependent manner and has been used for their purification. Since ACC-1 binds both bovine brain isozymes (61- and 63-kDa forms) and ACAP-1 recognizes only the 61-kDa isozyme, ACAP-1 can be used to separate and purify the two brain isozymes. The procedures described here for phosphodiesterase isolation from brain are rapid and require few enzymatic assays, resulting in preparations of good purity, specific activity, and yield (Tables II, III). The procedures for brain tissue can be easily adapted for use with larger amounts of tissue. The cross-reactivity of ACP-1 for rat brain phosphodiesterase suggests that this antibody may recognize isozymes from other mammalian tissues.

Reproductive life of French-Canadians in the 17-18th centuries: a search for a trade-off between early fecundity and longevity.

One of the predictions derived from Williams' (1957) evolutionary theory of senescence is the existence of a trade-off between early fecundity and longevity. The population register of the French immigrants to Québec in the 17th century and of the first Canadians in the 17th and 18th centuries was used to detect such a trade-off in a noncontraceptive human population living at a time when longevity had not been prolonged by medical care and was not artificially shortened by wars, epidemics, or other external causes. No evidence for such a trade-off could be detected in these populations which had not yet reached the demographic transition phase (i.e., the historical period when longevity began to be extended and the progeny began to be reduced). Results are discussed in connection with the various studies aiming to test the Williams' theory.

Glycosylation reduces the bioactivity of calcitonin.

The biological significance of peptide hormone glycosylation is uncertain. To examine the effect of Asn-linked glycosylation on calcitonin's bioactivity we purified glycosylated calcitonin from a transplantable rat medullary thyroid carcinoma. Glycosylated calcitonin constituted 2.3% of the total extracted immunoreactive calcitonin. The structure of this peptide differed from nonglycosylated calcitonin only by the oligosaccharide modification of asparagine 3. Affinity of glycosylated calcitonin for lentil lectin indicated that the oligosaccharide was a complex processed form. In a standard in vivo bioassay glycosylated calcitonin had a markedly reduced hypocalcemic activity compared to nonglycosylated calcitonin, an effect most likely due to the presence of the oligosaccharide.

High refractive errors and the accident/incident rate in Canadian medical category 1 pilots.

BACKGROUND: Since 1982, the Canadian Civil Aviation Medicine Division has medically certified to Category 1 standard commercial and airline transport pilots whose visual correction was in excess of +/- 3.5 diopters (D). METHOD: A review between the years 1982 and 1991 of the 253 pilots who had been medically certified, although they were outside the standard, was conducted. We determined if there was any difference in the accident/incident rate in this group as compared with the Canadian general aviation population standardized to a rate per 100,000 flying hours. The 253 pilots were divided into two groups with Group A having a refractive error outside the range +/- 5.7 D and Group B having a refractive error range of +/- 3.5 to +/- 5.6 D. RESULTS: The Group A rate was within the expected range of accidents and incidents per 100,000 flying hours. The accident/incident rate in Group B was significantly lower than the expected average. CONCLUSION: In conclusion, the Canadian Civil Aviation Medicine Division's policy on granting "flexibility" to applicants with moderate to high refractive errors has not affected adversely the accident or incident rate and therefore has not compromised aviation safety.

Mediastinitis due to Gram-negative bacteria is associated with increased mortality.

The aim of this study was to describe the features of a large cohort of patients with postoperative mediastinitis, with particular regard to Gram-negative bacteria (GNB), and assess their outcome. This bicentric retrospective cohort included all patients who were hospitalized in the Intensive Care Unit with mediastinitis after cardiac surgery during a 9-year period. Three hundred and nine patients developed a mediastinitis with a mean age of 65 years and a mean standard Euroscore of six points. Ninety-one patients (29.4%) developed a GNB mediastinitis (GNBm). Of the 364 pathogens involved, 103 GNB were identified. GNBm were more frequently polymicrobial (44% versus 3.2%; p <0.001). Being female was the sole independent risk factor of GNBm in multivariate analysis. Initial antimicrobial therapy was significantly more frequently inappropriate with GNBm compared with other microorganisms (24.6% versus 1.9%; p <0.001). Independent risk factors for inappropriateness of initial antimicrobial treatment were GNBm (OR = 8.58, 95%CI 2.53-29.02, p 0.0006), and polymicrobial mediastinitis (OR = 4.52, 95%CI 1.68-12.12, p 0.0028). GNBm were associated with more drainage failure, secondary infection, need for prolonged mechanical ventilation and/or use of vasopressors. Thirty-day hospital mortality was significantly higher with GNBm (31.9 % versus 17.0%; p 0.004). GNBm was identified as an independent risk factor of hospital mortality (OR = 2.31, 95%CI 1.16-4.61, p 0.0179).

[An essay on Quebec's demographic development from 1534 to 2034]. / Essai sur l'evolution demographique du Quebec de 1534 a 2034

PIP: A general review of the development of the population of Quebec since 1534 is presented in the form of separate summaries for each 50-year period. Topics discussed include sources of data, estimates of the North American Indian population, and estimates of immigration. Some consideration is given to projections to the year 2034. (summary in ENG, SPA)^ieng

[The French character of the pioneers of the Saint Lawrence valley]. / Le caractere francais des pionniers de la vallee laurentienne.

The origin of migrants to the Saint Lawrence valley in Canada prior to 1765 is explored. The author presents data concerning the sex and language distribution of the migrant population. "Immigrants who settled in the Saint Lawrence valley before 1765 were [primarily of] French origin. Many came from provinces where, at least in the rural areas, French was still not the dominant language. Pioneer families who arrived before 1680 had a relatively large linguistic homogeneity. Close to 40% originated from large or medium sized cities, and this proportion is close to 50% in the case of women." (SUMMARY IN ENG AND SPA)