scholarly journals Degredation of insulin by a particulate fraction from adipose tissue

1970 ◽  
Vol 116 (5) ◽  
pp. 825-831 ◽  
Author(s):  
Kenneth Sumner ◽  
Richard J. Doisy
Keyword(s):  
Adipose Tissue ◽  
Paper Chromatography ◽  
Trichloroacetic Acid ◽  
Degradation Products ◽  
Enzyme System ◽  
Enzyme Concentration ◽  
Particulate Fraction ◽  
Alkaline Ph ◽  
Ph Optimum ◽  
Rat Adipose Tissue

The destruction of 125I-labelled insulin by an enzyme system from rat adipose tissue was studied. The system was located in the particulate fraction. Activity was assayed by the amount of 125I-labelled degradation products rendered soluble in trichloroacetic acid. The system was heat-labile, with an alkaline pH optimum. The velocity of the reaction varied directly with the enzyme concentration. Paper chromatography of the degradation products showed six ninhydrin-sensitive areas with radioactivity coinciding with three of them. Albumin inhibited the system; ribonuclease did not. Although only 25% of the total 125I-label was detected by this assay, results with insulin-specific assays suggested that most (80–90%) of the hormone was inactivated. Possible interpretations of these results are discussed. The particulate fractions of other tissues were also studied.

THE WHEAT LEAF PHOSPHATASES: V. SOME PROPERTIES OF THE ENZYME SYSTEM HYDROLYZING β-GLYCEROPHOSPHATE IN CRUDE JUICE PREPARATIONS

1963 ◽  
Vol 41 (1) ◽  
pp. 113-120 ◽  
Author(s):  
D. W. A. Roberts
Keyword(s):  
Enzyme System ◽  
Enzyme Concentration ◽  
Ph Optimum ◽  
Wheat Leaf ◽  
Excess Substrate

Wheat leaf press juice contains an enzyme that has β-glycerophosphatase activity, which has a pH optimum close to pH 5.7. The enzyme is inhibited by orthophosphate, pyrophosphate, and 10−4 M fluoride. Fluoride inhibition can be abolished by thorough dialysis. Fluoride partially protects the enzyme from denaturation by heat.Enzyme kinetics shows that the log of the enzyme concentration is proportional to the log of the rate of liberation of orthophosphate from the substrate in the presence of excess substrate (0.2 M to 0.6 M) at pH 5.7. This observation can be used for quantitation of the enzyme.

THE WHEAT LEAF PHOSPHATASES: V. SOME PROPERTIES OF THE ENZYME SYSTEM HYDROLYZING β-GLYCEROPHOSPHATE IN CRUDE JUICE PREPARATIONS

1963 ◽  
Vol 41 (1) ◽  
pp. 113-120 ◽  
Author(s):  
D. W. A. Roberts
Keyword(s):  
Enzyme System ◽  
Enzyme Concentration ◽  
Ph Optimum ◽  
Wheat Leaf ◽  
Excess Substrate

Wheat leaf press juice contains an enzyme that has β-glycerophosphatase activity, which has a pH optimum close to pH 5.7. The enzyme is inhibited by orthophosphate, pyrophosphate, and 10−4 M fluoride. Fluoride inhibition can be abolished by thorough dialysis. Fluoride partially protects the enzyme from denaturation by heat.Enzyme kinetics shows that the log of the enzyme concentration is proportional to the log of the rate of liberation of orthophosphate from the substrate in the presence of excess substrate (0.2 M to 0.6 M) at pH 5.7. This observation can be used for quantitation of the enzyme.

Effects of insulin on amino acid and ribonucleic acid metabolism in rat adipose tissue

1962 ◽  
Vol 202 (4) ◽  
pp. 605-610 ◽  
Author(s):  
Bruce M. Carruthers ◽  
Albert I. Winegrad
Keyword(s):  
Adipose Tissue ◽  
Ribonucleic Acid ◽  
Trichloroacetic Acid ◽  
Acid Metabolism ◽  
Tissue Protein ◽  
Carbon 14 ◽  
Rat Adipose Tissue ◽  
Fat Pads ◽  
Precipitable Protein

Trichloroacetic acid precipitable protein and ribonucleic acid were isolated from paired pools of rat epididymal fat pads after in vitro incubation. Insulin in vitro, without glucose, had no effect on the incorporation of carbon from uniformly labeled glycine-C14, l-proline-C14 or l-histidine-C14 into adipose tissue protein. In the presence of as little as 0.1 µm/ml of unlabeled glucose, insulin markedly increased the incorporation of carbon from these three amino acids into protein. Insulin in vitro also increased the incorporation of carbon from glucose-U-C14 into both ribonucleic acid and protein. The recovery of C14 derived from glucose-6-C14 in the ribonucleic acid of adipose tissue relative to that from glucose-1-C14 was increased when insulin was present. Insulin increased the incorporation of C14 from pyruvate-2-C14 into adipose tissue protein in the absence of added glucose. The addition of glucose had no effect on the recovery of C14 from pyruvate-2-C14 when insulin was present. Carbon-14 from pyruvate-2-C14 was incorporated into ribonucleic acid, but insulin did not increase its incorporation.

scholarly journals Protease and ribonuclease activities in bovine pituitary lobes

1971 ◽  
Vol 123 (2) ◽  
pp. 153-162 ◽  
Author(s):  
J. C. Pickup ◽  
D. B. Hope
Keyword(s):  
Trichloroacetic Acid ◽  
Posterior Pituitary ◽  
Neurosecretory Granules ◽  
Alkaline Ph ◽  
Inhibitory Effects ◽  
Ph Optimum ◽  
Exogenous Rna ◽  
Absorbing Material ◽  
Endogenous Substrate ◽  
Alkaline Ribonuclease

1. Acid and alkaline protease activities in bovine anterior and posterior pituitary lobes were reinvestigated by measurement of u.v. and Folin–Ciocalteu colour values of trichloroacetic acid-soluble digestion products of denatured haemoglobin. 2. Both lobes of the pituitary gland contain a cathepsin with a pH optimum at 3.8. 3. When release of u.v.-absorbing material was used as the assay there was also an optimum at pH8.3–9.7, but this proved to be due to the release of nucleosides from an endogenous substrate. 4. The presence of a `cyclizing' ribonuclease active at alkaline pH on endogenous RNA was confirmed by the inhibitory effects of phosphate, arsenate and bentonite. The activity was unaffected by heat, EDTA or metal ions. The enzyme also acted on exogenous RNA. 5. A purified preparation of neurosecretory granules from fresh bovine posterior pituitary lobes was free from alkaline ribonuclease activity. Most of the activity present in the tissue was recovered in the supernatant plus microsomal material. 6. The distribution of RNA did not follow that of the alkaline ribonuclease.

Fatty acid esterifying enzymes in rat adipose tissue homogenates

1968 ◽  
Vol 46 (9) ◽  
pp. 1039-1045 ◽  
Author(s):  
Anna M. Daniel ◽  
David Rubinstein
Keyword(s):  
Fatty Acids ◽  
Adipose Tissue ◽  
Fatty Acid ◽  
Acid Phosphatase ◽  
Chain Length ◽  
Significant Alteration ◽  
Ph Optimum ◽  
Tissue Homogenates ◽  
Rat Adipose Tissue

Some characteristics of enzymes in homogenates of rat adipose tissue concerned with esterification of fatty acids have been investigated. Acyl-CoA thiokinase is the most active of the enzymes studied, with optimal concentrations of palmitate and ATP being 2 mM and 25 mM respectively. The thiokinase has a pH optimum between 8 and 10 and reacts with fatty acids ranging in chain length from C4 to C22, with the greatest activity towards palmitate. About 50% of the activity is found in the 100 000 × g supernatant. Acyl-CoA : α-glycerolphosphate acyltransferase and acyl-CoA deacylase have pH optima between 7 and 8. Albumin at a concentration of 1% activates the former, while the latter is inhibited by concentrations of albumin greater than 0.5%. Deacylase activity is found almost entirely in the 100 000 × g supernatant. Both the acyl-CoA : α-glycerolphosphate acyltransferase and the acyl-CoA : diglyceride acyltransferase lose much of their activity upon fractionation. The pH optimum of the acyl-CoA : diglyceride acyltransferase ranges from pH 7 to 9, while that of the phosphatidc acid phosphatase is 6. The latter enzyme is distributed equally between particulate and soluble portions of the homogenate. When these enzymes are assayed in homogenates from fed and fasted animals, a significant alteration is found only in the level of acyl-CoA deacylase, which is decreased. The properties of these enzymes can be related to the extent and type of esterification in homogenates from fed and fasted animals.

scholarly journals Rat epididymal adipose tissue acetyl-CoA carboxylase

1970 ◽  
Vol 48 (8) ◽  
pp. 915-921 ◽  
Author(s):  
P. R. Desjardins ◽  
K. Dakshinamurti
Keyword(s):  
Adipose Tissue ◽  
Epididymal Adipose Tissue ◽  
Acetyl Coa Carboxylase ◽  
Acetyl Coa ◽  
Ph Optimum ◽  
Epididymal Fat ◽  
Ph Dependent ◽  
Rat Adipose Tissue ◽  
Cold Inactivation ◽  
Fat Pads

The properties of a partially purified acetyl-CoA carboxylase (acetyl-CoA:CO2 ligase (ADP), EC 6.4.1.2) from rat epididymal fat pads have been studied. The properties of the rat adipose tissue enzyme are similar to those of the liver in regard to the pH optimum and affinity for substrates and inhibitors. The rat adipose tissue carboxylase shows a pH-dependent, reversible cold inactivation.

scholarly journals Effects of age and cell size on rat adipose tissue metabolism.

1975 ◽  
Vol 16 (6) ◽  
pp. 461-464 ◽  
Author(s):  
G Holm ◽  
B Jacobsson ◽  
P Björntorp ◽  
U Smith
Keyword(s):  
Adipose Tissue ◽  
Cell Size ◽  
Adipose Tissue Metabolism ◽  
Tissue Metabolism ◽  
Rat Adipose Tissue
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