Malate transport in Schizosaccharomyces pombe.

The transport of malate was studied in a Schizosaccharomyces pombe wild-type strain and in mutant strains unable to utilize malic acid. Two groups of such mutants, i.e., malic enzyme-deficient and malate transport-defective mutants, were differentiated by a 14C-labeled L-malate transport assay and by starch gel electrophoresis followed by activity staining for malic enzyme (malate dehydrogenase [oxaloacetate decarboxylating] [NAD+]; 1.1.1.38) and malate dehydrogenase (1.1.1.37). Transport of malate in S. pombe was constitutive and strongly inhibited by inhibitors of oxidative phosphorylation and of the formulation of proton gradients. Transport was a saturable function of the malate concentration. The apparent Km and Vmax values for transport by the parent were 3.7 mM and 40 nmol/min per mg of protein, respectively, while those of the malic enzyme-deficient mutant were 5.7 mM and 33 nmol/min per mg of protein, respectively. Malate transport was pH and temperature dependent. The specificity of transport was studied with various substrates, including mono- and dicarboxylic acids, and the possibility of a common transport system for dicarboxylic acids is discussed.