Phosphoenolpyruvate carboxylase decarboxylation catalyzed reaction in cytosol of rat adipose tissue

O. Meyuhas*, Ch Boshwitz, L. Reshef

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

The activity of phosphoenolpyruvate carboxylase (ITP:oxaloacetate carboxylyase (transphosphorylating) in crude extracts of adipose tissue and liver was measured in the direction of phosphoenolpyruvate formation. Knowledge of the maximal rate of this process under these conditions is of importance in the evaluation of the physiological significance of changes in enzyme level induced by various treatments. The substrate (oxaloacetate) may be added either directly or generated (a) from malate catalyzed by malate dehydrogenase (l-malate:NAD+ oxidoreductase, EC 1.1.1.37) in the presence of NAD+ and pyruvate, (b) from aspartate and α-ketoglutarate, catalyzed by aspartate aminotransferate (l-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1, formerly known as glutamate:oxaloacetate transaminase). All these yielded a similar maximal activity. With the adipose tissue enzyme, the Km value for oxaloacetate, whether supplied directly or generated was 2.2·10-5 M. With liver enzyme a similar Km value was obtained only if oxaloacetate was generated, while a higher value (3·10-4 M) was found by directly adding oxaloacetate. Both oxaloacetate and malate, at high concentrations inhibit phosphoenolpyruvate carboxylase activity. The inhibition of the adipose tissue enzyme, but not the liver enzyme, may be overcome by the addition of pyruvate. In the presence of pyruvate, vmax for phosphoenolpyruvate formation was attained with 3·10-3 M malate, as a source of oxaloacetate. Half maximal activity was found with 2.3·10-4 M malate. This concentration of malate is physiological and therefore implies that the activity of the enzyme in vivo rarely exceeds its half maximal activity.

Original languageEnglish
Pages (from-to)224-237
Number of pages14
JournalBBA - Enzymology
Volume250
Issue number1
DOIs
StatePublished - 20 Oct 1971

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