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Biomedical subjects

R Julien

Publications and source records attributed to R Julien.

At least 109 records · Page 6Linked to original sources
PubMed1981

Horse pancreatic lipase. Interaction with colipase from various species.

Horse pancreatic lipase has been purified from tissue homogenates. Molecular and catalytic properties of horse lipase are comparable to those of the pancreatic lipases previously isolated. Kinetic studies of the inhibition of horse lipase activity by bile salts and of reactivation by pure colipase from three species (horse, ox and pig) allowed to calculate the apparent dissociation constant (Kd) of the lipase-colipase complex in the presence of the substrate (triolein). Identical values of Kd were found in all three cases (Kd = 1.1 10(-9) M). These values are lower by several orders of magnitude than that published for the binding between lipase and colipase in the absence of substrate. Qualitative experiments show that the activation of horse lipase can be accomplished by rat, dog and chicken colipase as well. The interaction between lipase and colipase is enhanced when the complex is adsorbed at the lipid-water interface. This specific protein-protein interaction is preserved in heterologous mixtures using colipases from other animal species.

Animals↗
PubMed1980

New relations for activity analysis of associating enzymes.

New relations for catalytic-activity analysis are proposed for simple association/dissociation equilibria between the mono- and oligo-meric forms of enzymes in the case where these equilibria evolve very slowly in comparison with the binding of the substrates. This analysis of activity versus total enzyme concentration leads rapidly to information, complementary to that given by physico-chemical methods, on specific activities, the degree of polymerization of the enzyme forms and on their dissociation constants.

Enzymes↗
PubMed1980

Interaction of porcine pancreatic colipase with a nonionic detergent, Triton X-100: spectrophotometric studies.

Strong perturbation of the ultraviolet spectrum of the tyrosines of porcine pancreatic colipase A is observed in the presence of Triton X-100 at concentration above the critical micellar concentration. Spectrophotometric titration of the phenolic groups of the protein shows that the apparent pKa value for two tyrosines is about 10.3, while the third tyrosine has a higher pKa value above 11.6. This residue is still protonated at pH 13 in the presence of Triton X-100. All perturbations induced by the nonionic detergent can be interpreted as resulting from interactions between colipase and Triton X-100 molecules at a hydrophobic site of the protein that includes the tyrosine residues. Results obtained in studies with Triton X-100 are similar to those already reported by Sari et al. (Eur. J. Biochem. 58:561 (1975) on the interaction of colipase with taurodeoxycholate. It is likely that the binding of both types of detergent occurs at the same specific site on the protein molecule. Data presented in this communication give further support to the hypothesis that a hydrophobic domain (residues 49-57), including all three tyrosines of the colipase molecule, participate to the well characterized interaction of the lipase cofactor with triglycerides at lipid-water interfaces.

Animals↗
PubMed1980

Simultaneous radioimmunoassay of androstenedione, dehydroepiandrosterone and 11-beta-hydroxyandrostenedione in plasma.

A simultaneous radioimmunoassay for delta 4-androstenedione (delta 4), dehydroepiandrosterone (DHA) and 11 beta-hydroxyandrostenedione (11 beta OH delta 4) in plasma is described. This involved preparing first an anti-11 beta-hydroxyandrostenedione-3-0-carboxymethyl oxime/BSA antiserum which binds both delta 4 and 11 beta OH delta 4, and an anti-dehydrosterone-7-0-carboxymethyl oxime/BSA antiserum. A chromatographic step using celite minicolumns separates these three steroids. The method was applied to the measurement of the plasma basal values of these three androgens in control subjects. Mean concentrations (ng/ml) of delta 4, DHA and 11 beta OH delta 4 were respecstively 1.35, 6.63 and 3.13 in males; 1.35, 6.65 and 2.59 in premenopausal females; 0.46, 1.53 and 1.38 in post-menopausal females, and 0.39, 0.73 and 1.78 in children 1--6 years of age. Dynamic tests were also carried out: ACTH stimulation was found to increase delta 4, DHA and 11 beta OH delta 4. Dexamethasone had a reverse effect causing a 50% diminution in delta 4 levels, a marked decrease in DHA levels, and a 90% decrease in 11 beta OH delta 4 levels. Metyrapone test was found to produce a 223% increase in delta 4 levels, a 196% increase in DHA levels, and a decrease of more than 90% in the 11 beta OH delta 4 levels. Estroprogestative drug treatment was accompanied by a decrease of not only delta 4, but also of DHA and 11 beta OH delta 4. Preliminary clinical results concerning these steroids show a parallel increase or decrease of delta 4 and 11 beta OH delta 4 in adrenal pathology. In ovarian hyperandrogeny, delta 4 is increased and 11 beta OH delta 4 is unchanged.

Adrenocorticotropic Hormone↗
PubMed1980

Adrenocortical 11 beta-hydroxylation defect in adult women with postmenarchial onset of symptoms.

Four cases in adults of a deficiency in the 11 beta-hydroxylation of corticosteroids were investigated by both basal and dynamic biological studies. Symptoms varied from patient to patient; hirsutism, menstrual disturbance, acne, deepening of the voice, and arterial hypertension appeared post puberty. Basal testing demonstrated elevated levels of plasma androgens. These include delta 4-androstenedione (patients, 3.80-6.43 ng/ml; normal, 1.33 +/- 0.33 ng/ml), urinary 17-ketosteroids (patients, 11.8-16.7 mg/24 h; normal, 5-10 mg/24 h), and urinary dehydroepiandrosterone. The basal tests were often insufficient to show the accumulation of the precursors (especially 17-hydroxyprogesterone) which are often given as evidence for an increase in ACTH stimulation. In studying the levels of the mineralocorticoids, there was shown to be an increased basal level of tetrahydrodeoxycorticosterone (patients, 142-317 microgram/24 h; normal, 60-80 microgram/24 h) which was raised by ACTH stimulation. These results, therefore, confirm the characteristic partial enzyme defect and give evidence for the heterogeneity of this syndrome. Based on the above observations, we believe it is appropriate to rename this condition adult adrenocortical 11 beta-hydroxylation defect rather than late-onset congenital adrenal hyperplasia.

17-Ketosteroids↗
PubMed1980

[Night sleep study in acute and chronic psychosis (author's transl)].

A group of 22 psychotics (19 schizophrenics) was recorded in acute and/or chronic phase by series of 3 consecutive nights. Our main purposes were to study correlations between subgroups and sleep patterns and to follow the clinical evolution of these patients in looking at the quantitative and/or qualitative modifications of the various sleep states. Schizoaffective psychotics showed a lack of the "first night effect". The patients recorded in acute and in remission phases differ from unmedicated normal subjects: the former had less deep sleep and more "intermediate phases": the later presented an increase, sometimes very high, of REM total duration. Finally, within each subgroup, the analysis of individuals pointed out, for some of them, an evolution opposite to the general tendency.

Adult↗
PubMed1977

[Methionyl-tRNA synthetase from wheat embryo: dissociation into subunits (author's transl)].

Wheat -embryo methionyl-tRNA synthetase is a dimeric protein of beta2 structure. When highly diluted, it loses the capacity to catalyze ATP-[32P]PPi exchange and to aminoacylate tRNAMet: at low enzymatic concentrations the rates of formation of[32P]ATP and [14C]methionyl-tRNAMet are lower than those predicatedby extrapolating the rates determined at higher enzyme concentrations. The difference between observed and expected rates becomes greater with decreasing enzyme concentration. Filtration of purified, dilute enzyme preparations on Sephadex G-200 results in the separation of dimer and monomer fractions. The proportion of monomer present increases with increasing pre-incubation times before the assay and demonstrates an equilibrium between active dimers and being shifted towards the production of monomers. Datapreviously gathered for Escherichia coli prolyl-tRNA synthetase and for bovine-pancreatic tryptophanyl-tRNA synthetase, coupled with the present results, suggests that the dissociation of dimeric synthetases may be a general phenomenon in eukaryotes as well as in prokaryotes. The number of sub-units and the dissociation constant were obtained at equilibrium, according to relations adapted to the case of oligomeric enzymes (KD congruent to 13 nM at 25 degrees C and pH 7.5). Rate constants were determined by kinetic studies of the attainment of equilibrium. The rate constant k1 for monomolecular dissociation was determined to be 1.85- 10-3 s-1 and k2 for the bimolecular association to be 0.145 - 106 M-1 s-1. The KD calculated from k1 and k2 was coherent with the experimentally determined value, at equilibrium. The sub-unit interactions, which involve only a small quantity of energy (delta G degree congruent to + 11 kcal mol-1; +45 kJ mol-1) at 25 degrees C, depend on the ionic environment of the medium and the presence of substrates. Alkaline pH favors monomer production, while the presence of methionine, (Mg-ATP)2- and tRNAMet protect the synthetase from dissociation. 2-mercaptoethanol and dithioerythritol prevent only slightly the loss of activity. Bovine serum albumin, however, protects the enzyme from dissociation under dilute conditions.

Amino Acyl-tRNA Synthetases↗
PubMed1977

Pancreatic and microbial lipases: a comparison of the interaction of pancreatic colipase with lipases of various origins.

Conjugated bile salts inhibit the the hydrolysis of triglycerides (TG) by the lipases from Rhizopus arrhizus and Geotrichum candidum. This occurs for detergent concentrations similar to those which suppress the action of mammalian pancreatic lipases upon the same substrates. However, in opposition with what is observed with the latter enzymes, the activity is not restored by the addition of pancreatic colipase. Both pancreatic and R. arrhizus lipases are inactivated at tributyrin/water interface, but only the first enzyme is protected against this surface denaturation by the pancreatic cofactor. These observations suggest that colipases synthesized in mammalian pancreas display specific interaction towards the lipases made by the same organ.

Animals↗
PubMed1977

[Alterations of sleep caused by acute and chronic adminstration of lithium].

The sleep of 2 groups of subjects receiving lithium was studied. Ten normal controls after 17 days of lithium had a significant decrease of Paradoxical Sleep duration, with an increase of PS latency. A second group of 10 manic-depressive patients had received lithium for 22 +/- 6 months when they were recorded. They had a greater amount of slow wave sleep than the control group before lithium but the difference of PS duration was only related to a first night effect. Therefore sleep changes induced by lithium are different according to the duration of lithium administration. In any case they are less important than those induced by most of the anti-depressants.

Adult↗
PubMed1977

Characterization of Triton X 100 extracted colipase from porcine pancreas.

Colipase was isolated from porcine pancreas homogenate prepared in the presence of detergent (Triton X 100). After precipitation by ammonium sulfate and ethanol, the cofactor was purified by chromatography on SP-Sephadex in the presence of Triton X 100 and on DEAE-cellulose in the absence of detergent. Two molecular forms of porcine colipase were obtained. They represent 80 per cent (colipase A) and 20 per cent (colipase B), respectively, of the total colipase. Valine is the N-terminal residue of both proteins. Their aminoacid composition is similar to that found by Borgstrom for the two forms of porcine colipase. Determination of the sequence of the first sixteen residues at the N-terminal end of colipase A indicates that the cofactor undergoes no proteolytic degradation in this region of the molecule when extraction is carried out in the presence of detergent. The recovery of colipase is about 30 per cent.

Amino Acid Sequence↗
PubMed1976

[Phenylalanyl-tRNA synthetase of wheat embryos. Purification, molecular weight, structure, properties].

From wheat germ, a phenylalanyl-tRNA synthetase (E.C.6.1.1.20) has been isolated and purified 187 fold by means of ammonium sulfate fractionation (40-50 per cent) followed by Sephadex G-200 gel filtration, chromatographies on DEAE-cellulose and hydroxyapatite. The enzyme appears to be homogeneous on Sephadex G-200 molecular filtration and polyacrylamide gel electrophoresis. Molecular weight determinations by sucrose gradient centrifugation, gel filtration and gel electrophoresis give an average of 250 00 daltons. The enzyme is dissociated in 1 per cent sodium dodecyl sulfate into two different equimolar components of 80 000 and 50 000 daltons ; this result suggests that the phenylalanyl-tRNA synthetase has a subunit structure : alpha2 beta2. Dissociation with sodium dodecyl sulfate and dithiothreitol gives four other components, probably resulting from the breakdown of the subunits. Optima values of pH, Mg2+ and K+ concentrations, effect of SH-compnents, kinetic parameters have been determined in the aminoacylation reaction. Physical and catalytic properties of wheat germ phenylalanyl-tRNA synthetase appear very similar to those of the yeast and E. coli enzymes.

Amino Acyl-tRNA Synthetases↗