Expression of cDNAs encoding the precursor and the mature form of chicken mitochondrial aspartate aminotransferase in Escherichia coli.

Both the precursor and the mature form of chicken mitochondrial aspartate aminotransferase were synthesized in Escherichia coli. The precursor was found to sediment quantitatively together with insoluble cell material. In contrast, mature mitochondrial aspartate aminotransferase could be readily extracted from the cells and was indistinguishable from the enzyme isolated from chicken heart in all respects tested: specific activity 230 units mg-1; Mr 2 X 45,000; pI greater than 9; NH2-terminal sequence SSWWSHVEMG, the initiator methionine having been removed by the bacteria. Thus, the polypeptide chain representing mature mitochondrial aspartate aminotransferase is an autonomous folding unit which attains its functional spatial structure independently of the presence of the prepiece, trans-membrane passage, and proteolytic processing.