The oxidation of d-α-hydroxy acids in animal tissues

Publisher Website
Google Scholar
Abstract
Liver and kidney mitochondria oxidize D-lactate much faster than L-lactate, whereas pigeon-breast muscle mitochondria oxidize only the L-isomer. This is in agreement with Huennekens et al. (1951a, b), but their finding that liver and kidney contain a "racemase" enabling pigeon-muscle particles to oxidize D-lactate could not be confirmed. Reduction of dyes by kidney mitochondria in the presence of D-lactate is inhibited by metal-complex-forming agents and not stimulated by nicotinamide-adenine dinucleotide. A soluble D-[alpha]-hydroxy acid dehydrogenase has been extracted from rabbit-kidney-cortex mitochondria and partially purified. The enzyme, which occurs in liver and kidney in several animal species, catalyses oxidation of lactate and straight-chain homologues, glycerate, malate and tartrate; it was specific for the D-isomer whenever this could be tested. The product of D- lactate oxidation is pyruvate. With lactate and homologues, Km. /Vmax. is proportional to chain length. Electron acceptors include various ayes, ferricyanide and cytochrome c, but not oxygen. Nicotinamide -adenine dinucleotide is not needed. The enzyme when extracted has low activity, but undergoes activation during storage at 4[degree]. Inclusion of cyanide in the assay system causes immediate full activation. Possible metabolic roles of the enzyme are discussed.