The specificity of malic dehydrogenase from higher plants

Abstract

A method of purifying malic dehy-drogenase from pea epicotyls is described. A 50-fold purification was obtained by ammonium sulphate fractionation, treatment with calcium phosphate gel and chromatography on diethylaminoethylcellulose. Evidence is presented for the view that plant malic dehydrogenase, like the corresponding animal enzyme, is an a-hydroxydicarboxylic acid dehydrogenase. A number of kinetic constants have been evaluated. Slight differences between malic dehydrogenase prepared from mitochondria and from the supernatant remaining after removing mitochondria from a homogenate were noted. Two peaks with malic-dehy-drogenase activity were observed during chromatography but all pre-parations appeared to have the same substrate specificity.