Relative stabilities of purified human mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase in lyophilized materials

Abstract

Eight different pools of purified human mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase were prepared, to examine the effects of the following matrix variables: the matrix support material (bovine serum albumin and polyvinylpyrrolidone), endogenous pyridoxal concentration, and azide as an antimicrobial preservative. Storage temperatures of 25 and 37°C were used as a rapid and convenient means of accelerating the degradation process. Activity of the enzyme was measured with and without pyridoxal in the reaction solution. We found that the mitochondrial isoenzyme was consistently more labile than the cytoplasmic isoenzyme under identical storage conditions. Both isoenzymes were more stable in matrixes containing bovine serum albumin than in those containing polyvinylpyrrolidone. No apparent difference in the stability of either isoenzyme was observed at matrix pyridoxal concentrations of 15 μmol/L and 150 μmol/L. Only the mitochondrial isoenzyme in matrixes containing bovine serum albumin and 15 μmol of pyridoxal per liter had increased activity (about 9%) when pyridoxal was added to the enzymatic reagent. The amount of activity in reconstituted specimens did not apparently change after 72 h at 4°C.