EVOLUTIONARY ANALYSIS OF ASPARTATE AMINOTRANSFERASES

Aspartate aminotransferase isoenzymes are located in both the cytosol and organelles of eukaryotes, but all are encoded in the nuclear genom e. In the work described here, a phylogenetic analysis was made of asp artate aminotransferases from plants, animals, yeast, and a number of bacteria. This analysis suggested that five distinct branches are pres ent in the aspartate aminotransferase tree. Mitochondrial forms of the enzyme form one distinct group, bacterial aspartate aminotransferase formed another, and the plant and vertebrate cytosolic isoenzymes each formed a distinct group. Plant cytosolic isozymes formed a further gr oup of which the plastid sequences were a member. The yeast mitochondr ial and cytosolic aspartate aminotransferases formed groups separate f rom other members of the family.