Generation process of cytosolic aspartate aminotransferase molecular forms by several treatments

Abstract

α-, β-, and γ-forms of chicken liver cytosolic aspartate aminotransferase generate variants on storage (4°C, 25 days). The variants developed from each isolated form appeared as evenly spaced bands with increasing anodic mobilities after polyacrylamide gel electrophoresis (PAGE), pH 8.8, and specific staining. Their mobilities coincided with those of the more negatively charged forms present in fresh tissue. Development of faster-running variants on storage was avoided by addition of thiol reagents to the freshly isolated forms. In their presence, β- and γ-forms were partially transformed into one and two variants with lower anodic mobilities analogous to those of native α- and β-forms. Short pH and heat treatments did not modify the electrophoretic patterns of the α-, β-, and γ-forms, but the incubation with 5 mMl-ascorbic acid (37όC, 7h) produced more anodic active bands. The formation of these variants was inhibited by the presence, in the incubation mixture, of superoxide dismutase and catalase. The kinetic parameters of the forms submitted to the different treatments were similar to those of the freshly isolated subforms. The results obtained suggest that minor subforms of the enzyme could be generatedin vivo by a mechanism in which the oxidation of particular amino acid groups is involved.