Metabolism of Isolated Kidney Tubules

Abstract

Pyruvate dehydrogenase activity was measured in extracts of isolated kidney cortex tubules, prepared by collagenase treatment. The measured activities were comparable to those described previously for whole kidney homogenates.Incubation of tubules in vitro in the absence of exogenous substrates led to a steady increase in enzyme activity over 30 min. This increase was not significantly changed by the addition of several gluconeogenic substrates including lactate, glutamine, glutamate, glycerol, fructose and malate. 1 mM oleate, 5 mM acetate and 20 mM 2-oxoglutarate however, prevented this increase completely. I n contrast, glucose and dihydroxyacetone accelerated the activation of pyruvate dehydrogenase during incubation in vitro. 20 mM pyruvate very rapidly activated pyruvate dehydrogenase with a following decrease below the activity of control experiments without substrate. 1 mM oleate and 20 mM 2-oxoglutarate counteracted the increase in pyruvate dehydrogenase activity caused by glucose and dihydroxyacetone and had no effect in the presence of 20 mM pyruvate.Determination of the inactive part of pyruvate dehydrogenase after addition of purified pyruvate dehydrogenase phosphatase revealed that all changes observed were probably caused by enzymatic interconversion of pyruvate dehydrogenase.The results are compared with previously published observations on the regulationlof pyruvate dehydrogenase in vivo and confirm the role of fatty acids in the regulation of kidney ,cortex pyruvate metabolism. Enzymes. Pyruvate dehydrogenase (EC 1.2.4.1) ; Arylamine acetyltransferase (EC 2.3.1.5). and kidney cortex [5,7] the mechanism by which fatty acids depressed pyruvate oxidation was a matter of speculation. Inhibition of pyruvate dehydrogenase by increased levels of acetyl-CoA [4] and an increase in reduced nicotinamide-adenine dinucleotide have been discussed as possible metabolic mediators of the action of fatty acids. Although these mechanisms have been shown to operate in isolated mitochondria [S] and with purified enzyme preparations [9], their physiological importance was hard to prove in whole cells since intracellular compartmentalization of metabolites and cofactors prevented $ a n exact interpretation of measured overall levels.The

Differential Response of Liver and Kidney Adenine Nucleotide Translocase and Pyruvate Dehydrogenase Activity to Alloxan Diabetes

“…A significant aspect of the present study is the difference in response of the renal and hepatic enzymes to the diabetic state. Similar responses are seen in the two tissues with respect to the decreased PDH activity [9,10] (table I) and to the increased activity of pyru- acyl carnitine derivatives [26][27][28]. The paral lel changes that occur in liver and kidney in diabetes may thus be related to the increased utilization of fatty acids as the oxidized sub strate in this condition.…”

“…It has been shown repeatedly that fatty acids result in a diversion of pyruvate from an oxidative to a gluconeogenic route in both liver and kidney [9,10,26], There is consid erable discussion as to the exact mechanism of this effect, whether it is solely by alteration in the acetyl CoA/CoA and NADH/NAD+ quotients which affect the pyruvate dehydro genase kinase activity [2,4] or whether a more direct effect is located at PDH via the…”

The mode of regulation of pyruvate dehydrogenase of lactating rat mammary gland. Effects of starvation and insulin

“…Experiments in vitro indicate that an increased supply of long-chain fatty acids can lead to increased phosphorylation of pyruvate dehydrogenase in heart, liver and kidney (Wieland et al, 1971b;Patzelt et al, 1973;Guder & Wieland, 1974). Perfusion of isolated rat heart with acetoacetate had a similar effect (Wieland et al, 1971b).…”

13C‐NMR study of glycerol metabolism in rabbit renal cells of proximal convoluted tubules

“…In particular we wanted to examine more precisely whether glycerol does, in the end, also enter the glutamate/glutamine pool. In this context, in view of the known inhibiting influence of glycerol on pyruvate dehydrogenase [13], we wondered whether pyruvate carboxylase activity could be observed.…”