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)

Conditioned medium from Reuber H-35 or Fao hepatoma cells contains autocrine factors that both stimulate DNA synthesis and activate acetyl-coenzyme A (CoA) carboxylase in serum-deprived Fao cells. The factor(s), which appears within 4 h of serum-free culture, also increases the cell number and the mitotic index. The effects of the conditioned medium are insulinomimetic, both with respect to stimulation of DNA synthesis and acetyl-CoA carboxylase activity. However, no induction of tyrosine aminotransferase activity or stimulation of aminoisobutyric acid uptake is seen in response to the conditioned medium. Insulin over a 4-h period does not increase the concentration of DNA synthesis stimulating activity that is observed in the medium. This activity is dialyzable and is resistant to acid treatment or to heating to 60-100 degrees C and to trypsin digestion; it is not extracted with chloroform/methanol nor adsorbed by charcoal or by a C18 reverse-phase column. Fractionation of the conditioned medium derived from Reuber H-35 hepatoma cells by gel filtration chromatography reveals two low molecular weight (less than 1000) compounds that both stimulate DNA synthesis in Fao hepatoma cells. The larger compound (peak I) also stimulates the activity of acetyl-CoA carboxylase. The stimulatory effects of the peak I compound are destroyed by nitrous acid deamination, periodate oxidation, and methanolysis. Biosynthetic labeling studies indicate the probable presence of glucosamine, galactose, and perhaps phosphate in the peak I-activating material. No significant incorporation of either myoinositol or mannose into the active material has been observed. These data, taken together, are consistent with a glycan structure for this autocrine factor, which bears strong resemblance to similar insulinomimetic factors generated in BC3H1 myocytes and H-35 hepatoma cells in response to insulin and on digestion of membranes with a phosphatidylinositol-specific phospholipase C. Further characterization of this factor may provide insight into different pathways of insulin action and could provide a strategy to check autocrine-stimulated tumor growth.
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PMID:An autocrine factor from Reuber hepatoma cells that stimulates DNA synthesis and acetyl-CoA carboxylase. Characterization of biologic activity and evidence for a glycan structure. 289 65

The abilities of several nucleotides to protect tyrosine aminotransferase (L-tyrosine: 2-oxoglutarate aminotransferase, EC 2.6.1.5) against proteolytic inactivation in vitro have been examined as part of an ongoing investigation of the role of cyclic GMP in the intracellular degradation of the hepatic enzyme. Although neither cyclic GMP nor cyclic AMP was found to exert such a protective effect, certain nucleotide analogs were observed to inhibit the inactivation of tyrosine aminotransferase by trypsin and chymotrypsin. The nucleotides which conferred the strongest protection were the dibutyryl derivatives of cyclic GMP and cyclic AMP. This phenomenon appears to require a purine nucleotide with hydrophobic substituent(s), while the cyclic phosphate is not essential. The nucleotides probably act by direct interaction with tyrosine aminotransferase as indicated by changes in kinetic properties and heat stability of the enzyme and by their failure to inhibit trypsin when other protein substrates, including another aminotransferase, were used. Dibutyryl cyclic AMP was shown to block the appearance of a characteristic 43 kDa tryptic cleavage product of tyrosine aminotransferase but not the conversion of the native 54 kDa form to a size of 50 kDa. Arguments are presented against the involvement of the protective effect in the actions of dibutyryl cyclic nucleotides on tyrosine aminotransferase in cells.
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PMID:Protection of tyrosine aminotransferase against proteolytic digestion by nucleotide derivatives. 290 Jun 54

1. Relative rates of enzyme inactivation were measured in liver slices, homogenates and cytosol fractions as well as in the presence of trypsin and at acid pH. The enzymes chosen are all present in the cytosol fraction of rat liver, and have widely different degradation rate constants in vivo. 2. The inactivation rates of lactate dehydrogenase, fructose bisphosphate aldolase, glucose 6-phosphate dehydrogenase, glucokinase, phosphoenolpyruvate carboxykinase (GTP), l-serine dehydratase and thymidine kinase in liver preparations at neutral pH are in a similar order to the rate constants of degradation of these enzymes in the intact animal. 3. The two exceptions of this general correlation were tyrosine aminotransferase, which was stable in vitro but not in vivo, and glyceraldehyde phosphate dehydrogenase, which shows the reverse pattern. 4. These findings generally support the concept that the same factors are responsible for enzyme inactivation in vitro as occur in the intact tissue.
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PMID:The relative stability of liver cytosol enzymes incubated in vitro. 415 34

We have studied tyrosine aminotransferase in the liver of adult and old rats. Thermostability and trypsin action were not modified, and no charge differences have been found by isoelectric focusing between 'adult' and 'old' enzymes. Inducibility by glucocorticoids was increased in vivo in these 27- to 31-month-old rats, but not in vitro, in cultured hepatocytes. Moreover, we have shown the absence of 'cross-reacting material' for tyrosine aminotransferase in senescent rat livers. The rapid turnover of this enzyme may explain the apparent absence of alterations during aging.
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PMID:Tyrosine aminotransferase in senescent rat liver. 610 18

Tyrosine aminotransferase was induced in adult and senescent rat liver and its properties studied. We show the appearance of a 'cross-reacting material' for induced tyrosine aminotransferase of old rats compared to basal enzyme; this cross-reacting material can be provoked in adult rats after injection of cycloheximide, and suppressed in adult and old rats after injection of a serine protease inhibitor (tosylphenylalanine chloromethylketone). Other properties of induced tyrosine aminotransferase (thermostability, Km for tyrosine, isoelectrofocusing) are identical except for the proportion of the three forms and their sensitivity to trypsin in the absence of pyridoxal phosphate, which is increased in senescent animals. The suppression of cross-reacting material clearly indicates that it is not due to errors on old rat liver DNA but rather to post-translational modifications. This demonstrates also the role of serine proteases in tyrosine aminotransferase degradation. We suggest that induced enzyme of senescent rats would undergo a conformational change, possibly due to a release of pyridoxal phosphate from the enzymic molecules, which would thus become more susceptible to proteolytic attack than those of adult rats.
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PMID:Age-related changes of liver tyrosine aminotransferase in senescent rats. 610 90

Isolated liver cells, which were prepared from adult rats by a trypsin-liver-perfusion technique, were treated with dexamethasone or hydrocortisone at a concentration of 7.7 X 10(-6) M for 8 days in primary culture. The treated cultures displayed homogeneous population consisting of epithelial-like clear cells, while the untreated cultures displayed mixed population consisting of epithelial-like clear cells and fibroblast-like cells. The epithelial-like clear cells, which proliferated in the cultures treated with glucocorticoids for 8 days in primary culture, did not show any morphological changes following cultivation in glucocorticoid-free medium. After continuous glucocorticoid-treatment for more than 1 month, the treated cultures showed relatively low cell densities at confluence. The surface area of individual epithelial-like clear cells in the cultures treated with glucocorticoids for long periods of time was evidently greater than that in the cultures treated for only 8 days. The epithelial-like clear cells had glucose 6-phosphatase and tyrosine aminotransferase activities even though the levels of these enzyme-activities were very low compared with those in rat liver homogenates.
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PMID:Selective growth of epithelial-like clear cells from adult rat liver by short-term exposure to glucocorticoids in primary culture. 613 8

When trypsin-dissociated liver cells from 17-day chick embryos were grown in regular minimum essential medium, mixed hepatocyte-fibroblast cultures resulted. When D-valine was substituted for L-valine in this medium, fibroblast growth was suppressed, leaving virtually pure hepatocyte cultures. Tyrosine aminotransferase activity is induced by cortisol in mixed cultures. No induction of enzyme activity is observed with cortisol exposure to hepatocytes, grown in D-valine. However, when cortisol-containing medium is conditioned by pre-incubation with mixed cells and then transferred to hepatocytes, tyrosine aminotransferase activity is induced. Enzyme activity is also induced in mixed cells incubated in D-valine medium in the presence of cortisol. It appears that a substance produced in the presence of fibroblasts exposed to cortisol is capable of inducing tyrosine aminotransferase activity in hepatocytes. This activity, which we have termed fibroblast hepatocyte factor, is heat stable, of low molecular weight, and antigenically different from fibroblast pneumonocyte factor, a factor similar to that produced by lung fibroblasts exposed to cortisol.
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PMID:Evidence for epithelial-mesenchymal interactions mediating glucocorticoid effects in developing chick liver. Fibroblast-hepatocyte factor. 613 26

Induced tyrosine aminotransferase from adult and old rat liver was purified and its properties were studied. No differences could be detected for any physicochemical properties studied, i.e. specific activity, molecular weight, isoelectric point, thermostability, sensitivity to trypsin, Km for pyridoxal phosphate. Moreover, some age-related modifications previously described such as increased sensitivity to trypsin for induced old enzyme were no longer found. Tyrosine aminotransferase provides another argument against the 'error theory' of cellular aging.
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PMID:Properties of purified tyrosine aminotransferase from adult and senescent rat liver. 613 40

A cell-surface modulator with the ability to mimic the reciprocal effects of cell density on cell growth and liver-specific functions of mature rat hepatocytes in primary culture (Nakamura, T., Yoshimoto, K., Nakayama, Y., Tomita, Y., and Ichihara, A. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 7229-7233) was solubilized with 4% octyl glucoside and 4 M guanidine HCl from plasma membranes purified from adult rat liver. The membrane-free modulator showed activities for inhibition of DNA synthesis stimulated by insulin with epidermal growth factor and stimulation of tyrosine aminotransferase induction by dexamethasone. The apparent Mr of the factor was estimated as 670,000 by gel filtration on a Sephacryl S-400 column equilibrated with 0.5% octyl glucoside and 4 M guanidine HCl. The modulator was heat-labile and sensitive to trypsin. These results suggest that the reciprocal regulations of cell growth and hepatocyte-specific functions are mediated via cell to cell contact by a cell-surface modulator(s) that is an integral membrane protein.
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PMID:Reciprocal modulation of growth and liver functions of mature rat hepatocytes in primary culture by an extract of hepatic plasma membranes. 614 8

Primary cultures of liver cells isolated from adult rats by trypsin and collagenase perfusion techniques were carried out to compare cytologic and biochemical properties between the differently prepared cells. Trypsin-dispersed cells consisted of comparatively smaller cells, whereas collagenase-dispersed cells consisted of larger cells. The cell attachment efficiency on culture day 1 was about twice as high in the liver cells prepared with collagenase than those prepared with trypsin. Mature hepatocytes isolated by collagenase perfusion could be maintained in the primary culture for a longer period than those isolated by trypsin perfusion. Epithelial-like clear cells started to grow much earlier in the primary culture of the trypsin-dispersed liver cells than in that of the collagenase-dispersed liver cells. Earlier proliferation of epithelial-like clear cells could not be induced by in vitro trypsinization of the collagenase-dispersed liver cells. Both kinds of enzymatically prepared liver cells showed albumin production and exhibited glucose 6-phosphatase (D-glucose-6-phosphate phosphohydrolase, EC 3.1.3.9, G6Pase) and tyrosine aminotransferase (L-tyrosine: 2-oxoglutarate amino-transferase, EC 2.6.1.5, TAT) activities for 1 week in the primary culture. Albumin production was higher in the liver cells prepared with collagenase than those prepared with trypsin, whereas G6Pase activity was almost the same between them. TAT activity up to culture day 2 was about 3-fold higher in the liver cells prepared with collagenase than in those prepared with trypsin. Combined supplementation of dexamethasone (1 X 10(-5)M) and insulin (10 micrograms/ml) consistently improved the cell attachment efficiency and was very effective in the maintenance of mature hepatocytes in both types. Furthermore, these hormones enhanced the albumin production and TAT activity in both types.
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PMID:Comparison of cytologic and biochemical properties between liver cells isolated from adult rats by trypsin perfusion and those isolated by collagenase perfusion. 614 85


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