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Biomedical subjects

C Gagnon

Publications and source records attributed to C Gagnon.

At least 163 records · Page 9Linked to original sources
PubMed1981

Stimulus-secretion coupling in exocrine pancreas: role of protein carboxyl methylation.

The role of protein carboxyl methylation in amylase secretion from incubated rat pancreatic lobules was assessed. All the components of the carboxyl methylation system, protein carboxyl methylase, methyl-acceptor protein substrates, and protein methylesterase, were found in the rat pancreas. Protein carboxyl methylation is stimulated by both pancreozymin and carbachol at concentrations that are equally effective in stimulating amylase release. The secretagogue-enhanced increase in protein carboxyl methylation was concomitant with the onset of the secretory response. These responses were blocked by the receptor antagonists, dibutyryl cGMP and atropine. Inhibitors of protein carboxyl methylase inhibited carboxyl methylation stimulated by pancreozymin but did not affect the secretory response to the hormone. Ethyleneglycol-bis-(beta-aminoethylether)-N-N'-tetraacetic acid blocked protein carboxyl methylation and amylase release, indicating that extracellular calcium was essential for both processes. The presence or absence of calcium did not alter the enzyme activity in lobule homogenates. The data suggest that only a small part of the total cellular protein carboxyl methylation activity is directly involved in pancreatic enzyme secretion. Like the calcium requirement in secretion, protein carboxyl methylation also lies distal to the stimulant-receptor interaction.

Amylases↗
PubMed1980

The localization of protein carboxyl-methylase in sperm tails.

Protein carboxyl-methylase (PCM), an enzyme known to be involved in exocytotic secretion and chemotaxis, has been studied in rat and rabbit spermatozoa. PCM activity and its substrate methyl acceptor protein(s) (MAP) were demonstrated in the supernate after solubilization of the sperm cell membrane by detergent (Triton X-100). A protein methylesterase that hydrolyzes methyl ester bonds created by PCM was demonstrated in rabbit but not in rat spermatozoa. This enzyme was not solubilized by nonionic detergent. The specific activities of PCM in rat spermatozoa from caput and cauda epididymis were similar and lower than that found in testis. By contrast, MAP substrates were low in testis and increased in parallel with sperm maturation in the epididymis. Multiple MAP were demonstrated in spermatozoa by polyacrylamide gel electrophoresis. The pattern of these proteins was similar in spermatozoa from different portions of the reproductive tract. Fractionation of heads and tails of rat spermatozoa on sucrose gradients indicated that PCM was found exclusively in the tail fraction, whereas MAP was detected both in head and tail fractions. The presence of all the components of the protein carboxyl-methylation system in spermatozoa and the localization of PCM and some of its substrates in the sperm tail are consistent with their involvement in sperm cell motility.

Animals↗
PubMed1979

Protein carboxyl-methylation in rat testes: a study of inherited and X-ray-induced seminiferous tubule failure.

Protein carboxyl-methylase (PCM), the enzyme that transfers methyl groups from S-adenosyl-methionine to free carboxyl groups on proteins, is highly localized in testes. The cellular distribution of PCM and its substrates, the methyl acceptor proteins, was investigated. Separation of testicular cells on an albumin gravity gradient revealed the preferential localization of both enzyme and substrates in spermatids. In young rats, PCM activity increases with age coincidently with germ cell maturation. Rats which are heterozygous for the Hre gene (Hre/+) are infertile as a result of germ cell depletion. In these animals, testicular PCM specific activity and total activity were, respectively, 4--6 and 40--50 times lower than in normal testes. Enzyme activity in testes from animals with x-ray-induced germ cell depletion was also very low. These observations suggest that PCM is located in germ cells.

Animals↗
PubMed1978

Enzymatic methylation of carboxyl groups of chromaffin granule membrane proteins.

Carboxyl groups of membrane and soluble proteins from bovine adrenal medulla chromaffin granules were enzymatically methylated. The methylated peptides were resolved using gel electrophoresis under acidic conditions in the presence of N-cetylpyridinium chloride. There was a selective methylation of two groups of membrane peptides which did not correspond to any of the chromaffin granule soluble proteins. Dopamine beta-hydroxylase, an acidic protein accounting for up to 25% of the membrane proteins, was a poor substrate for protein carboxylmethylase. The methyl esters of membrane proteins were more labile than those of the chromaffin granule soluble proteins. At all pH values tested, membrane protein-methyl esters were hydrolyzed three times more rapidly than the soluble protein-methyl esters.

Adrenal Medulla↗
PubMed1978

[Actinomycetes antagonistic to fungi and not affecting Rhizobium meliloti].

The effects of 481 actinomycetes isolated from agricultural soils supporting good growth of alfalfa or clover on two efficient strains of Rhizobium meliloti A2 and S14 were studied. Strain A2 was inhibited by 28% of the isolates and strain S14 was inhibited by 31% of them. No significant difference was found between the resistance of both actinomycete strains. The effects of the 288 isolates not affecting R. meliloti on six fungi were also studied. The most sensitive fungus was Stemphylium sarcinaeforme inhibited by 20% of the isolates, while Fusarium culmorum was the most resistant fungus and was inhibited by only 6% of the isolates. Thirteen isolates inhibited four to six fungi. In an autoclaved greenhouse soil, isolate 181 which inhibited the six fungi tested significantly reduced the population of the phytopathogenic fungus F. oxysporum f. sp. medicaginis and eliminated the inhibitory effect showed by this fungus on strain A2 of R. meliloti.

Actinomycetales↗
PubMed1978

Beta adrenergic stimulation of protein carboxymethylation and amylase secretion in rat parotid gland.

Protein carboxymethylase (S-adenosyl-l-methionine:protein-O-methyltransferase, EC 2.1.1.24) transfers methyl groups from S-adenosylmethionine to protein carboxyl groups. This cytosolic enzyme is found in highest concentration in secretory tissue and methylates membrane proteins. Stimulation of the parotid gland by catecholamines rapidly and reversibly increases protein carboxymethylase activity and methyl acceptor capacity of proteins in parotid homogenates. Isoproterenol was effective at concentrations causing amylase release in vivo and in vitro. Both enzyme activity and methyl acceptor capacity of proteins increased within 5 min, continued to increase for 30 min and then declined to control values within 60 min. The response to isoproterenol was stereospecific. The action of isoproterenol could be blocked by the beta adrenergic antagonist propranolol, while the alpha adrenergic agonist phenylephrine did not stimulate the enzyme or increase methyl acceptor proteins. Methyl acceptor proteins have been partially characterized by polyacrylamide gel electrophoresis. Although many proteins in the parotid are methylated, only two groups of methylated proteins increase after stimulation by isoproterenol.

Amylases↗
PubMed1977

Selective induction of tyrosine hydroxylase and dopamine beta-hydroxylase by nerve growth factor: comparison between adrenal medulla and sympathetic ganglia of adult and newborn rats.

Administration of NGF to newborn and adult rats elicits a selective increase in TH and DBH both in sympathetic ganglia and adrenal medulla. This effect does not depend on intact preganglionic cholinergic fibers. The augmented enzyme activity results from enhanced enzyme synthesis since it can be abolished by cycloheximide and NGF has been shown to enhance the incorporation of [3H]leucine into DBH molecules. The responsiveness of the adrenal medulla to NGF is also supported by light and electron microscopic autoradiograms which show that intravenously injected 125I-NGF is accumulated with high selectivity in adrenal chromaffin as compared to adjacent adrenal cortical cells. In spite of the many similarities between the response of the adrenergic neurons and adrenal chromaffin cells to NGF, there are also two distinct differences. (a) In newborn rats the ratio between the TH increase effected by a single and 10 subsequent daily injections of NGF is 1:2 in the adrenal medulla and 1:7 in the superior cervical ganglia. (b) If adrenal medullae are transferred to organ culture after intravenous injection of NGF, maximal TH response is initiated 60-90 min after NGF administration. In superior cervical ganglia only a half-maximal response is initiated at that time. After a stationary phase a second increase starts after about 6 h to reach the maximum after 12 h. The biphasic time course of the initiation of TH induction by NGF in sympathetic ganglia is in agreement with the time course of 125I-NGF accumulation after intravenous injection27 reflecting the moiety of NGF reaching the cell bodies of the adrenergic neurons directly by the blood stream (initial accumulation) and by retrograde axonal transport (second phase).

Adrenal Medulla↗