Similar Changes In Enzyme Activity Research Articles

The effects of fasting and refeeding on liver glycogen synthase and phosphorylase in obese and lean mice.

The responses of hepatic glycogen synthase and phosphorylase to fasting and refeeding were assessed as part of an investigation into possible sites of insulin resistance in gold thioglucose (GTG) obese mice. The active forms glycogen synthase and phosphorylase (synthase I and phosphorylase a) and the total activity of these enzymes were estimated in lean and GTG mice over 48 h of food deprivation, and for 120 min after glucose gavage (1 g/kg wt). In lean mice there was a maximal reduction in hepatic glycogen content after 12 h of starvation and the activity of phosphorylase a decreased from 23.8 +/- 1.9 to 6.8 +/- 0.7 mumol/g protein/min. These changes were accompanied by an increase in the activity of synthase I (from 0.14 +/- 0.01 to 0.46 +/- 0.04 mumol/g protein/min). In obese mice, similar changes in enzyme activity occurred after 48 h of starvation. These changes were accompanied by a significant reduction in the hyperinsulinemia and hyperglycemia of the GTG mice. After glucose gavage in both lean and obese mice, the activity of synthase I further increased over the first 30 min and declined thereafter. The activity of phosphorylase a increased progressively after refeeding. Results from this study suggest that despite increased hepatic glycogen deposition, the responses of glycogen synthase and phosphorylase, in livers of obese mice, to fasting and refeeding are similar to those of control mice even in the presence of insulin resistance.

Effects of ciprofibrate and 2-[5-(4-chlorophenyl)pentyl]oxirane-2-carboxylate (POCA) on the distribution of carnitine and CoA and their acyl-esters and on enzyme activities in rats. Relation between hepatic carnitine concentration and carnitine acetyltransferase activity.

The effects of feeding the peroxisome proliferators ciprofibrate (a hypolipidaemic analogue of clofibrate) or POCA (2-[5-(4-chlorophenyl)pentyl]oxirane-2-carboxylate) (an inhibitor of CPT I) to rats for 5 days on the distribution of carnitine and acylcarnitine esters between liver, plasma and muscle and on hepatic CoA concentrations (free and acylated) and activities of carnitine acetyltransferase and acyl-CoA hydrolases were determined. Ciprofibrate and POCA increased hepatic [total CoA] by 2 and 2.5 times respectively, and [total carnitine] by 4.4 and 1.9 times respectively, but decreased plasma [carnitine] by 36-46%. POCA had no effect on either urinary excretion of acylcarnitine esters or [acylcarnitine] in skeletal muscle. By contrast, ciprofibrate decreased [acylcarnitine] and [total carnitine] in muscle. In liver, ciprofibrate increased the [carnitine]/[CoA] ratio and caused a larger increase in [acylcarnitine] (7-fold) than in [carnitine] (4-fold), thereby increasing the [short-chain acylcarnitine]/[carnitine] ratio. POCA did not affect the [carnitine]/[CoA] and the [short-chain acylcarnitine]/[carnitine] ratios, but it decreased the [long-chain acylcarnitine]/[carnitine] ratio. Ciprofibrate and POCA increased the activities of acyl-CoA hydrolases, and carnitine acetyltransferase activity was increased 28-fold and 6-fold by ciprofibrate and POCA respectively. In cultures of hepatocytes, ciprofibrate caused similar changes in enzyme activity to those observed in vivo, although [carnitine] decreased with time. The results suggest that: (1) the reactions catalysed by the short-chain carnitine acyltransferases, but not by the carnitine palmitoyltransferases, are near equilibrium in liver both before and after modification of metabolism by administration of ciprofibrate or POCA; (2) the increase in hepatic [carnitine] after ciprofibrate or POCA feeding can be explained by redistribution of carnitine between tissues; (3) the activity of carnitine acetyltransferase and [total carnitine] in liver are closely related.

Effects of exercise, detraining, starvation, and refeeding on lipogenic capacity of Osborne-Mendel rat.

Both starvation and refeeding and exercise and detraining are procedures that result in lowered lipid stores followed by their refilling. Rats subjected to these procedures were evaluated for their ability to produce hepatic biosynthetic reducing equivalents. Five-week-old male Osborne-Mendel rats were exercised on a motorized treadmill for 6 wk (final speed 27 m/min, 60 min/day, 6 day/wk) or kept sedentary. Exercised and sedentary rats were starved for 48 h or fed ad libitum. After treatments, some rats in each group were killed. Remaining exercised animals were detrained or detrained and refed. Remaining sedentary rats were refed. Activities of hepatic glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and malic enzyme were evaluated. Plasma glucose, triglyceride, insulin, liver triglyceride, and body composition were determined. Results indicate that changes in lipids stores associated with starvation and refeeding and exercise and detraining are not associated with similar changes in enzyme activity. Starvation resulted in lowered plasma glucose, triglyceride, and insulin. Starvation and all exercise treatments resulted in lowered carcass fat. Exercised rats who were starved for 48 h and then detrained and refed for 72 h had the greatest liver weights and percent liver triglycerides. This was not associated with similar changes in enzyme activity. Increased liver lipid and decreased carcass fat may indicate a redistribution of lipid stores in these animals.

Mucosal enzyme activities, with special reference to enzymes implicated in bicarbonate secretion, in the duodenum of rats with cysteamine-induced ulcers.

1. Duodenal mucosa was collected from control rats and from animals which had received cysteamine, cysteamine plus cimetidine or pentagastrin. Animals which received cysteamine with or without cimetidine developed acute duodenal ulcers. Cysteamine treatment resulted in gastric acid hypersecretion, which was largely abolished by concurrent cimetidine administration. 2. Activities of enzymes implicated in bicarbonate secretion, HCO3--activated ATPase, carbonic anhydrase and Na+ + K+-activated ATPase, were measured in the duodenal mucosa of control rats and animals 24 h after subcutaneous administration of cysteamine. Assays of these enzymes in duodenal mucosal homogenates from animals with cysteamine-induced ulcers showed significant decreases in HCO3--activated ATPase and carbonic anhydrase activities compared with controls. 3. Alkaline phosphatase activity also fell significantly in the cysteamine-treated animals, and possibly reflects the HCO3---activated ATPase activity in the brush-border membrane. In contrast, activities of other marker enzymes from the brush-border membrane and from several intracellular organelles were unchanged, indicating an absence of gross organelle pathology in this experimental model. 4. Similar changes in enzyme activity were not caused by treatment with pentagastrin. Administration of cimetidine with the cysteamine did not protect the animals against ulceration, and the activity of HCO3--activated ATPase was persistently decreased. However, the carbonic anhydrase activity was unaltered in this latter group, compared with controls. 5. These findings suggest that in cysteamine-induced duodenal ulceration both gastric acid hypersecretion and impaired duodenal resistance occurs. It is suggested that decreased activities of key enzymes implicated in HCO3--secretion may reflect the biochemical basis for the decreased mucosal resistance.

Correlation between G-6-PDH Activity of the Erythrocytes and the Sex Chromatin Frequency in the Somatic Cells in New-Born Girls

It was demonstrated in investigations performed in 44 new-born girls, that the G-6-PDH activity of the erythrocytes gradually decreases up to the seventh day of life. This process goes hand in hand with the increase of sex chromatin, i.e. of heterochromaticchromosomes. These phenomena can be indirectly ascribed to the estrogens. No similar changes in enzyme activity were found in 28 new-born boys investigated as controls.

Regulation der UDPG-pyrophosphorylaseaktivit�t in Acetabularia

It has already been shown that in the uninucleate green alga Acetabularia mediterranea, a close relationship in time exists between cap formation and the activity of the enzyme UDPG-pyrophosphorylase. The activity of the enzyme increases strongly when cap formation sets in. Similar changes in enzyme activity are observed in nucleate and anucleate cells. It is very likely that the increase in the activity of the UDPG-pyrophosphorylase during cap formation is a result of increased synthesis of the enzyme (Zetsche, 1968). In addition to the correlation in time between cap formation and enzyme activity, there exists a close correlation in space which is expressed in terms of a polar distribution of the enzyme. The activity of the enzyme is highest in the apical region of the cell, whereas toward the basal end it decreases sharply. This apico-basal gradient of enzyme activity is especially strong in cells with a cap. By means of several experiments it was excluded that the above results were the consequence of an unequal distribution of inhibitors or activators of enzyme activity or of a differential inactivation of the enzyme during homogenization. We therefore conclude that the differences in enzyme activity between various regions of the cell are based upon differences in the amount of the enzyme present within these regions. Further experiments clearly demonstrated that the polar distribution of the enzyme is the result of a preferential synthesis of the enzyme in the apical region of the stalk. The rate of enzyme synthesis is higher within the apical region than in the middle and basal region, and this is particularly evident at the time of onset of cap formation. We conclude that the messenger-RNA responsible for the synthesis of the UDPG-pyrophosphorylase is distributed in the form of an apico-basal concentration gradient. If we accept the existence of such a gradient, then this implies that the messenger-RNA which is synthesized within the nucleus in the rhizoidal end of the cell must be transported over a distance of 60 mm in a polar direction toward the tip of the stalk and must be accumulated there. Unequal distribution of messenger-RNA thus may represent an important factor in the morphogenesis of the cell. However it remains to be shown how such a distribution is brought about.