Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.4 (trypsin)
42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Regression of MTW9 mammary carcinoma, which consistently follows withdrawal of mammotropic hormones, was characterized by a rapid decrease of thymidine incorporation into DNA but only a slight reduction or uridine incorporation into RNA and amino acid incorporation into proteins. Within 24 hr of hormone withdrawal, cytosol proteins of MTW9 became more easily degraded by trypsin, alpha-chymotrypsin, or subtilisin BPN'. Labilization of cytosol proteins occurred much earlier than any change in the level of protein synthesis or lysosomal enzyme activity. The data showing increased susceptibility to proteolysis could not be explained either by the presence of endogenous proteases, by the destruction of the exogenous proteases used in the assay, or by the existence of protease inhibitors. Nor were any differences detected either in the distribution of radioactive precursor among the cytosol proteins from growing or regressing tumors or in the electrophoretic pattern of the same proteins. Preincubation of the cytosol proteins with dithiothreitol or with prolactin, 17 beta-estradiol, progesterone, and hydrocortisone did not modify the susceptibility to proteolysis. However, after heat denaturation, cytosol proteins of regressing and growing tumors became equally susceptible to proteolysis. It is suggested that regression of MTW9 mammary carcinoma occurs not only because cell reproduction is arrested, but also because susceptibility of cytosol proteins to proteolysis is increased.
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PMID:Increased susceptibility of cytosol proteins to proteolytic digestion during regression of a hormone-dependent mammary tumor. 83 67

The C-terminal undecapeptide of ovine prolactin, H-Leu-Asn-Cys-Arg-Ile-Ile-Try-Asn-Asn-Asn-Cys-OH possesses several structural features common to protein proteinase inhibitors, yet has no inhibitor properties. The undecapeptide is completely hydrolysed by trypsin (Arg-Ile bond) and by chymotrypsin (Tyr-Asn bond), with a proteolytic coefficient of approximately 3,000 M-1 sec-1 and 240 M-1 sec-1 respectively. On the basis of these results, a consideration of entropy, and studies by other workers, we agree with the view of Nishino et al. that the best models for small synthetic peptides with inhibitor properties would be those naturally-occurring inhibitors whose reactive site is located within a small disulphide loop.
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PMID:A study of proteinase inhibition by simulation of inhibitor reactive site regions: interaction of the C-terminal undecapeptide of ovein prolactin with some proteinases. 85 30

Three methionine-modified derivatives of ovine prolactin have been prepared: two by oxidation of the methionines by H2O2 to sulfoxide (partial and complete), and the third by complete alkylation of the metionines with iodoacetic acid to the carboxymethyl sulfonium salts. The derivatives were characterized by exclusion chromatography, amino acid composition, circular dichroism spectra, relative rates of digestion by trypsin, and biological activity. Partially oxidized prolactin, having four of its seven methionines oxidized, was very similar to the native hormone. The unmodified methionines in partially oxidized prolactin were found to be the residues at positions 36, 81 and 132. The prolactin derivatives in which all the methionines had been oxidized, or alkylated, showed major changes in all parameters examined. In addition, circular dichroism spectra indicated that complete modification of all the methionines in prolactin exposes the normally buried tryptophans.
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PMID:Studies on pituitary prolactin. 39. Reaction of the ovine hormone with hydrogen peroxide. 95 54

Different tissues of the black sea bream Mylio macrocephalus including the liver, gills, intestine, muscle, gonad, swim bladder, spleen, heart and kidney were examined for the presence of prolactin and growth hormone receptors. Membranes were prepared from the tissues and 125I-labeled ovine prolactin and bovine growth hormone were used as ligands. It was found that the liver contained the highest level of specific 125I-labeled ovine prolactin and bovine growth hormone binding, suggesting the existence of hepatic prolactin and growth hormone receptors. The protein nature of the hepatic growth hormone receptor was revealed by the reduction of specific 125I-labeled growth hormone binding after treatment of hepatic membranes with trypsin and chymotrypsin.
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PMID:The sea bream liver contains receptors for growth hormone and prolactin. 141 25

Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analyses we have identified immunoreactive prolactin (PRL) proteins with molecular weights of 24 and 16 kD in the female rat brain. Because PRL target tissues have been shown to contain enzymes which, in vitro, cleave PRL into a 16-kD PRL fragment, studies were performed to characterize PRL proteolysis in the female rat brain. In vitro proteolysis of PRL was examined by incubating [125]I-PRL with 25,000 g subcellular fractions followed by SDS-PAGE under reducing conditions. At acidic pHs, incubation of PRL with 25,000 g hypothalamic fractions consistently resulted in the generation of a 16-kD fragment. The generation of the 16-kD fragment was time and tissue concentration dependent. Enzyme inhibitor analysis indicated that PRL proteolysis could be blocked by aspartate and serine protease inhibitors, but not sulfhydryl, metalloenzyme or trypsin protease inhibitors. Subcellular localization of hypothalamic PRL proteolytic activity by equilibrium density centrifugation revealed a bimodal distribution of proteolytic activity with modal densities of 1.12 and 1.24 g/ml. Homogenization of the tissue in a hypo-osmotic medium disrupted the high density peak resulting in a single low-density peak at the top of the gradient. These data indicate that subcellular fractions of the rat brain contain enzymes which can cleave PRL into a 16-kD fragment under acidic conditions. The majority of the enzymatic activity is localized in membrane-bound particles with a density similar to subcellular particles which contain PRL.
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PMID:Proteolytic modification of prolactin by the female rat brain. 147 17

To elucidate the role of steroid hormones in the synthesis and secretion of prolactin (PRL), a mammotroph-enriched cell preparation was made by centrifugal elutriation of trypsin-dispersed anterior pituitary cells from adult male rats. The mammotrophs were enriched by about 2-fold in comparison with those in the initial cell suspension. On the other hand, the ratio of enrichment of gonadotrophs, thyrotrophs and somatotrophs was less than onetenth. The separated mammotrophs were incubated in media containing 17 beta-estradiol and/or progesterone. 17 beta-estradiol increased the levels of PRL in the medium and the cells of 300% and 140%, respectively, and the content of messenger RNA (mRNA) to 193%, whereas progesterone had no such effects. Furthermore, progesterone had no influence on the 17 beta-estradiol-induced increase in the levels of PRL and the contents of PRL mRNA. These results suggest that 17 beta-estradiol regulates PRL synthesis and secretion in mammotrophs, whereas progesterone does not.
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PMID:Indirect effects of progesterone on the synthesis and secretion of prolactin in mammotroph-enriched cells. 162 94

The biochemical mechanism of action of prolactin is unknown. This hormone enters the blood stream and binds to receptors predominantly in the monomeric form. A structural analysis of mammalian and piscine prolactin based on the present-day concepts of proteolytic processing of the hormone molecules in target tissues has been carried out. The experimental data suggest that prolactin molecules are protected from exopeptidase influence by their terminal cyclic peptides. The highly conservative proline-2 residues increase the resistance of the mammalian hormone N-terminal fragment to the effects of many aminopeptidases. Structurally the C-terminal cyclic peptides of prolactin, growth hormone and placental lactogen were shown to be homologous to peptides inhibiting trypsin-like proteinases. A structural analysis of the N-terminal domain of mammalian prolactin revealed the important role of Pro-2 and Pro-4 residues at positions adjacent with and inside the disulfide moiety. It is assumed that these proline residues and the cyclic structure are necessary for the manifestation of the inhibiting effect of the mammalian prolactin N-terminal dodecapeptide on proline-specific proteinases. It is assumed that proteolytic degradation of prolactin molecules in target tissues may induce the secretion of functionally active peptides.
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PMID:[Analysis of the structure of prolactin terminal fragments as potential substrates of serine and proline-specific proteinases]. 174 7

The primary structure of growth hormone (GH) isolated from the adenohypophysis of the bullfrogs (Rana catesbeiana) was determined. The hormone was reduced, carboxymethylated and subsequently cleaved with cyanogen bromide. Intact bullfrog GH was also digested with lysyl endopeptidase and trypsin. The resulting fragments were separated by reverse-phase high-performance liquid chromatography and subjected to sequence analysis using an automated gas-liquid sequencer employing the Edman method. Bullfrog GH was found to consist of 190 amino acid residues. The amino acid sequence determined is in accord with that deduced from bullfrog GH cDNA by Pan and Chang (1988) except for nine residues at positions 43-48, 73, 80 and 87. Sequence comparisons revealed that bullfrog GH is more similar to tetrapod GHs (e.g., 69% homology with sea turtle GH, 66% with chicken GH and 61% with ovine GH) than to GHs of teleosts (e.g., 35% homology with chum salmon GH and 33% with bonito GH) except for eel (52% identity). Bullfrog GH and prolactin exhibit a sequence homology of 25%.
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PMID:The complete amino acid sequence of growth hormone of the bullfrog (Rana catesbeiana). 185 28

Dopamine has a catechol group which can be easily oxidized by mild oxidizing agents. Ascorbic acid has been routinely added to a dopamine solution in order to protect it from oxidation. We have examined the effect of ascorbic acid on dopaminergic inhibition of prolactin release. Male rat pituitary cells were dispersed using trypsin and cultured for 5-7 days before experiments. Ascorbic acid did not stimulate nor inhibit prolactin release in both static monolayer culture and dynamic perifusion systems, but potentiated by approximately 100 times the inhibitory effect of dopamine on prolactin release. In order to differentiate chemical protection from potentiation, we tested the potentiation effect of isoascorbic acid which is an epimer of biologically active L-ascorbic acid but is biologically less active. Our results indicated that isoascorbic acid caused less potentiation of the dopaminergic effect on prolactin release than did ascorbic acid. In a perifusion system, a high concentration of dopamine (100 nmol/l) was unable to inhibit prolactin release for a 1 h experimental period, but a low concentration of dopamine (10 nmol/l) plus ascorbic acid (10 mumol/l) inhibited prolactin release for the entire 1 h perifusion period. There is a strong possibility that ascorbic acid may be a physiological supplementary agent for the prolactin-release inhibiting factor (PIF) since the blood concentration of ascorbic acid is rather high (23-85 mumol/l).
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PMID:Ascorbic acid potentiates the inhibitory effect of dopamine on prolactin release: a putative supplementary agent for PIF. 197 18

A large number of studies have been performed concerning dopamine's inhibitory effect on prolactin release, but many of these studies have examined the effect of dopamine dissolved in a solution containing ascorbic acid. Ascorbic acid, routinely used to protect dopamine from oxidation, alone does not stimulate or inhibit prolactin release, but it can potentiate the inhibitory effect of dopamine in a static monolayer culture system by approximately 100 times. We have closely examined the inhibitory effect of dopamine on prolactin release in the absence of ascorbic acid using a perifusion system. Male rat adenohypophyses were dispersed with trypsin and cultured in a Petri dish to form cell clusters. Inhibition of prolactin release by dopamine (1 mumol/L) in the absence of ascorbic acid was sustained for only 63 min during the 2-h perifusion period. Following a 2-h period of incubation of dopamine in the same experimental solution, the dopamine concentration was reduced from 1 to 0.18 mumol/L, yet this "2-h-old dopamine" was still effective in inhibiting prolactin release (approximately 30 min). This result suggests that the lactotrophs may be desensitized by chronic exposure to a high concentration of dopamine in the absence of ascorbic acid. In contrast, when a low concentration of dopamine (3 nmol/L) containing ascorbic acid (0.1 mmol/L) was perifused, inhibition of prolactin release was sustained for the entire 2-h perifusion period. Although there may be a large number of explanations for dopamine's transient inhibitory effect on prolactin release, the present results suggest that dopamine may require supplementary agent(s) to effectively inhibit prolactin release and thus function as the prolactin release inhibitory factor (PIF).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Reexamination of dopamine as the prolactin-release inhibiting factor (PIF): supplementary agent may be required for dopamine to function as the physiological PIF. 198 Apr 29


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