The distribution of
aspartate aminotransferase activity in yeasts was determined. The number of species of the
enzyme in each yeast was determined by zymogram analysis. All the yeasts, except for the genus Saccharomyces, showed two or three activity bands on a zymogram. From among the strains, Rhodotorula minuta [corrected] and
Torulopsis candida were selected for examination of the existence of yeast mitochondrial
isoenzymes, because these strains showed two clear activity bands on the zymogram and contained a high amount of the
enzyme. Only one
aspartate aminotransferase was purified from T. candida: the component in the minor band on the zymogram was not an
isoenzyme of
aspartate aminotransferase. On the other hand, two
aspartate aminotransferases were purified to homogeneity from R. minuta [corrected]. The components in the main and minor activity bands on the zymogram were identified as the mitochondrial and cytosolic
isoenzymes, respectively, in a cell-fractionation experiment. The enzymatic properties of these
isoenzymes were determined. The yeast mitochondrial
isoenzyme resembled the animal mitochondrial
isoenzymes in molecular weight (subunits and native form), absorption spectrum, and substrate specificity. The
amino acid composition was closely similar to that of pig mitochondrial
isoenzyme. Rabbit antibody against the yeast mitochondrial
isoenzyme, however, did not form a precipitin band with the pig mitochondrial
isoenzyme.