Studies on a mevaldic acid reductase of rat liver*

Abstract

A TPNH-specific mevaldic reductase of rat liver has been partially purified. This enzyme fraction catalyzes the reduction of both optical isomers of mevaldic acid to isomeric mevalonic acids. Although the evidence is not unequivocal, most data are in agreement with the conclusion that a single enzyme mediates the reduction of the two isomers of mevaldic acid. The enzyme is strongly inhibited by hydroxylamine, but it is unaffected by iodoacetamide and only weakly inhibited by p-chloromercurisulfonic acid and N-ethyl maleimide. The enzyme exhibits no metal ion requirement and has a rather broad pH optimum (6.5 to 7.7). The biologically active isomer of mevaldic acid is reduced much more rapidly than the other isomer, and, in the reductive process, one mole of mevaldic acid is reduced and one mole of TPNH is oxidized for each mole of mevalonic acid formed. Biological activity of the enzymatic reduction product is demonstrated by its conversion to terpenol pyrophosphates and by its utilization as substrate for mevalonic kinase. Possible metabolic roles for the enzyme and its substrate are discussed. A second aldehyde-reducing activity was detected, which is DPNH specific and has activities similar to alcohol dehydrogenase. This enzyme shows significant activity in the oxidation of geraniol and farnesol in the presence of DPN.