The Cytosolic and Mitochondrial Aspartate Aminotransferases from Pig Heart: A Comparison of their Primary Structures, Predicted Secondary Structures and Some Physical Properties

Abstract

1. A primary structure is presented for mitochondrial aspartate aminotransferase from pig heart based on previously published results [Barra et al. (1977) FEBS Lett. 83, 241–244; Doonan et al. (1979) Ital. J. Biochem. 28, 441–455; Barra et al. (1979) Ital. J. Biochem. 28, 456–477, 478–490] and a small amount of extra information given here. 2. A detailed comparison is made between the primary structures of the cytosolic and mitochondrial isozymes. These are homologous proteins with 47% identity of primary structure and do not differ appreciably in overall polarity. 3. Hydrophobic chromatography of the isozymes using alkyl agaroses suggests that the cytosolic but not the mitochondrial isozyme has a hydrophobic patch or pocket capable of binding to the alkyl side chains of the affinity medium. 4. Evidence is presented to show that the cytosolic isozyme contains some basic amino acids whose ionizations are not expressed under native conditions. The mitochondrial isozyme does not show this effect. 5. Predictions of the secondary structures of the isozymes are presented based on four predictive models. Minimum predictions are derived on the basis of agreement of three out of four of the individual predictions. These agregate predictions underestimate the amount of ordered secondary structure in both isozymes and suggest a relatively low degree of similarity between the isozymes. Individual predictive models, on the other hand, reveal greater similarities in secondary structures between the two isozymes. Copyright © 1980, Wiley Blackwell. All rights reserved