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Query: HUMANGGP:034761 (insulin)
 211,843 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

There is a description of the determination of the enzymatic activity of acid proteinases: the method is based on the use of 125J-labelled natural protein substrates. Labelled albumin 125J, globulin 125J, and insulin 125J were tested for the determination of activities. All the substrates were hydrolyzed with the enzymes of the supernatant fraction (106 000 g) of beff liver homogenate in the zone of acid pH. Optimum comditions of enzymatic reaction were tested, the dependence of reaction on the concentration of the enzyme, on time, and on temperature was determined, pH optimum was ascertained for individual substrates, and pH stability was determined. It follows from the results that the method is suitable for the determination of the enzymatic activity of proteinases of the cathepsin character.
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PMID:[Determination of the proteolytic activity of beef liver by means of natural substrates labed with 125 I]. 0 Aug 41

The effect of insulin was investigated in the isolated guinea pig liver perfused with Krebs-Ringer bicarbonate buffer containing red blood cells and albumin. In the mitochondria isolated from livers perfused with 10 units of insulin per hour, the phosphorylative activity with glutamate as a substrate increased to about 160 per cent of control 60 minutes after the beginning of perfusion (p less than 0.01). Such an enhanced phosphorylative activity was accompanied by increases in the respiratory control ratio, state 3 respiration, and P/O ratio. On the other hand, in the liver perfused with insulin, the levels of the energy charge and adenine nucleotide quotient increased to a significant degree as compared to the liver without insulin (p less than 0.01 and p less than 0.05, respectively). It is suggested that insulin plays an important role as a portal factor in regulating mitochondrial oxidative phosphorylation and the levels of the phosphorylated adenine nucleotides.
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PMID:Effect of insulin on mitochondrial oxidative phosphorylation and energy charge of the perfused guinea pig liver. 0 1

The fluorescnece porperties of 1,8-TNS in relation to the polarity and viscosity of the solvents have been studied and found to be just as useful as those of its positional isomer 2,6-TNS in the capacity of being a fluorescent probe. The properties of the hydrophobic region of insulin, des-pentapeptide (B26-30)- insulin (DPI), bovine plasma albumin, lysozyme, and ovalbumin have been investigated by employing this fluorescent probe. It has been shown that there is a small but definite hydrophobic region in DPI just as in insulin. This suggests that removal of the C-terminal pentapeptide does not impair seriously the hydrophobic structure related to the binding with insulin receptor. However, at physiologic pH, the hydrophobic region of DPI becomes more exposed than that of insulin and its conformation is less stable. As the pH is increased, the local conformation of the DPI molecule probably suffers some distortion, which damages the conformation of the hydrophobic region to a certain extent. In comparison with insulin, the DPI molecule is relatively loose and unstable.
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PMID:Structural studies on des-pentapeptide (B26-30)-insulin. IV. A preliminary investigation on the hydrophobic region by employing a fluorescence probe, 1-p-toluidinylnaphthalene-8-sulphonate. 1 Jun 23

A system of preparation of rat hepatocytes with extended viability has been developed to study the role of hormones and other plasma components upon secretory protein synthesis. Hepatocytes maintained in minimal essential medium reduced the levels of all amino acids in the medium except the slowly catabolized amino acids leucine, isoleucine, and valine, which steadily increase as the result of catabolism of liver protein. Although the liver cells catabolize 10-15% of their own protein during a 20-h incubation, the cells continue to secrete protein in a linear fashion throughout the period. The effects of insulin, cortisol, and epinephrine on general protein synthesis, and specifically on fibrinogen and albumin synthesis, have been tested on cells from both normal rats and adrenalectomized rats. Cells from normal animals show preinduction of tyrosine amino transferase (TAT), having at the time of isolation a high level of enzyme which shows only an increase of approximately 60% upon incubation with cortisol. In contrast, cells from adrenalectomized animals initially have a low level of enzyme which increases fourfold over a period of 9 h. The effects of both epinephrine and cortisol on protein synthesis are also much larger in cells from adrenalectomized animals. After a delay of several hours, cortisol increases fibrinogen synthesis sharply, so that at the end of the 20-h incubation, cells treated with hormone have secreted nearly 2.5 times as much fibrinogen as control cells. The effect is specific; cortisol stimulates neither albumin secretion nor intracellular protein synthesis. The combination of cortisol and epinephrine strongly depresses albumin synthesis in both types of cells. Insulin enhances albumin and general protein synthesis but has little effect on fibrinogen synthesis.
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PMID:Plasma protein synthesis by isolated rat hepatocytes. 1 83

Systematic analysis of the hydrolysis of benzyloxycarbonyl (Cbz)-dipeptides by cathepsin A [EC 3.4.12.1] purified from rat liver lysosomes showed that multiple forms of cathepsin A preferentially cleave peptide bonds with leucine, methionine, and phenylalanine. Cbz-Met-Met, -Met-Phe, -Phe-Met, and -Phe-Ala were hydrolyzed 6 to 8 times faster than the standard substrates, Cbz-Glu-Phe and Cbz-Glu-Tyr. The pH optima of the hydrolyses were 4.6 to 5.8. Hydrolysis of peptide bonds with glycine, isoleucine, and proline was very slow, but the rate depended on the nature of the adjacent amino acids. Proteins such as albumin, cytochrome c, gamma-globulin, hemoglobin, histone, myoglobin, and myosin were scarecely degraded. Peptide hormones, such as glucagon and adrenocorticotropic hormone (ACTH) were hydrolyzed markedly with optimum pH's of 4.5 and 4.6, respectively. Angiotensin I, II, bradykinin, Lys- and Met-Lysbradykinin (kallidin and Met-kallidin), and substance P were also hydrolyzed at appreciable rates. pH optima for these peptide hormones were 5.2 to 5.6. On the other hand, insulin and its A chain, luteinizing hormone-releasing hormone (LH-RH), oxytocin and vasopressin were cleaved slowly. In the hydrolyses of glucagon and other peptides, multiple forms of rat liver lysosomal cathepsin A again showed a carboxypeptidase nature, cleaving peptide bonds sequentially from the carboxyl terminal. Almost all of the amino acids were cleaved on prolonged incubation. Vaso-activites of angiotensin II and bradykinin were rapidly lost on hydrolysis by cathepsin A. Lysosomal cathepsin C [dipeptidylaminopeptidase I, EC 3.4.14.1] also activated angiotensin II, but did not inactive bradykinin. Cathepsin A, therefore, can be regarded as one of the lysosomal angiotensinases and kinases. No distinct differences were observed between the multiple forms of cathepsin A in these hydrolyses and inactivations of peptides.
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PMID:Studies on cathepsins of rat liver lysosomes. III. Hydrolysis of peptides, and inactivation of angiotensin and bradykinin by cathepsin A. 1 61

Inhibition of glucose-stimulated insulin release by exogenous insulin has been demonstrated in pancreatic islets to be associated with a decrease of the NADPH/NADP ratio and the pentose-phosphate cycle activity. Batches of five islets were incubated for 15 and 90 minutes in 1 ml. of KRB buffer with 2 per cent albumin containing 3 mg./ml. glucose and 0, 200, 400, or 800 microU./ml. of rat insulin, and the glucose-6-phosphate (G6P) and 6-phosphogluconate (6PG) contents were determined by enzymatic cycling. In response to a rise in the concentration of insulin, the 6PG/G6P ratio decreased. A close relationship was observed between this decrease of 6PG/G6P ratio and the net insulin release, the absolute rate of glucose oxidation via the pentose phosphate cycle, and the NADPH/NADP ratios measured under similar conditions. The results suggest that exogenous insulin, directly or indirectly, regulates the pentose cycle activity in the pancreatic islets at the G6P dehydrogenase step.
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PMID:6-Phosphogluconate/glucose-6-phosphate ratio in rat pancreatic islets during inhibition of insulin release by exogenous insulin. 1 30

The effect of various hormones on cytological and biochemical properties of cultured hepatic cells were investigated in order to obtain long-term survival of the hepatocytes with adult liver functions in primary culture. Insulin supplementation of the culture medium enhanced the attachemnt efficiency of cells in primary culture without affecting either maintenance of morphological characters of epithelial cells or retention of liver-specific functions in cultured cells. A combination of dexamethasone and insulin was apparently effective in stimulating the formation of a monolayer of polygonal cells with granular cytoplasm and in maintenance of liver-specific functions for relatively longer periods. Supplementation with either dexamethasone or hydrocortisone alone enhanced tyrosine aminotransferase activities in cultured cells for at least 4 days postinoculation. These steroid hormones also allowed growth of small epithelial cells with clear cytoplasm and maintenance of increased albumin production for 8 days after inoculation. The roles of these hormones in the primary culture of isolated hepatic cells are discussed in the present paper.
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PMID:Primary culture of adult rat liver cells. III. Hormonal effects on cytological and biochemical properties of primary cultured cells. 2 50

Acetyl coenzyme A carboxylase and fatty acid synthetase activities were studied to determine the biochemical basis of the markedly impaired capacity of fat cells from spontaneously obese, old rats to convert glucose to fatty acids relative to cells from lean, young rats. Michaelis constants for the substrates of both enzymes were similar in large and small adipocyte homogenates. In contrast, Vmax values were over 80% less in homogenates from large relative to small cells on a per cell basis. Long-term dialysis or the presence of albumin during the assays failed to restore the activities of these enzymes in homogenates of large fat cells. The combination of equal volumes of homogenates from the two cell types resulted in carboxylase and synthetase activities intermediate between activities found in the two homogenates alone. Therefore, the presence of endogenous allosteric inhibitors does not appear to account for the markedly blunted fatty acid synthesis enzyme activities in large fat cells. These results suggest that the fatty acid synthesis impairment, which is a primary defect in the insulin resistance of the large cells, is at least partly due to diminished cellular contents of acetyl coenzyme A carboxylase and fatty acid synthetase.
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PMID:Diminished activities of fatty acid synthesis enzymes in insulin-resistant adipocytes from spontaneously obese rats. 3 25

The isolated rat liver perfused for 12 hours at pH 7.10 with a suspension of bovine erythrocytes in Krebs-Ringer bicarbonate buffer containing 3 per cent bovine serum albumin has been used as a test system to study effects of glucagon and of dexamethasone in the presence and absence of insulin on net biosynthesis of rat serum albumin, fibrinogen, alpah1-acid glycoprotein, alpha2-(acute phase) globulin, and haptoglobin. Quantitative measurement of perfusate glucose, amino acid nitrogen, and urea affords a basis for determining net glucose and nitrogen balance in the perfusion system. Although the dose of dexamethasone (total 1.0 mug.) used was insufficient to induce synthesis of alpha2-acute phase globulin, net syntheses of albumin, fibrogen, alpha1-acid glycoprotein, and haptoglobin were increased. Glucagon given with dexamethasone depressed albumin and haptoglobin synthesis markedly, but not that of fibrinogen and alpha1-acid glycoprotein. Glucagon with dexamethasone markedly enhanced ureogenesis and glycogenolysis and elicited an exaggerated negative nitrogen balance. The unfavorable effects of glucagon on albumin and haptoglobin synthesis and on nitrogen balance were reversed by giving insulin simultaneously. It is emphasized that insulin is essential for positive nitrogen balance.
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PMID:Direct effects of glucagon on protein and amino acid metabolism in the isolated perfused rat liver. Interactions with insulin and dexamethasone in net synthesis of albumin and acute-phase proteins. 6 Nov 40

When Vero cells, a line derived from and African Green Monkey kidney, are grown under conditions where the saturation density is limited by serum, they deplete the growth medium of a factor necessary for cell division. The factor is a component of serum. When Vero cells are plated at low density (2 X 10(4)/cm2) in this depleted growth medium (after dialysis against serum-free Dulbecco's Modified Eagle's Medium) they initiate an unbalanced program of growth. Protein synthesis proceeds at the same rate as parallel cells in fresh serum, and and the cells accumulate protein as a function of time. DNA synthesis is also initiated in these cells, and the amount of DNA per cell increases for the next four days plating. However the cells quickly stop dividing. Measurements of DNA per cell using microspectrofluorometry show that the cells are accumulating in the late S and G2 period during this time. Thus we conclude that these cells cannot pass through a transition point in G2. When fresh serum is added to cells after three days in depleted growth medium, they divide before they begin to synthesize DNA. This further confirms that they are in late S and G2. Cell division is promoted in Vero cells in depleted growth medium by bovine fetuin, and to a lesser extent by bovine albumin. Cell division is not promoted by insulin, hydrocortisone, dexamethasone, linolenic acid, calcium, and typsin inhibitor form ovomucoid. From these data we conclude that transit through G2 requires the prescence of an extracellular factor.
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PMID:A serum factor requirement for the passage of cultured Vero cells through G2. 6 56


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