Aspartate aminotransferase activity and isoenzyme proportions in human liver tissues

Aspartate aminotransferase (EC 2.6.1.1) activity and the distribution of its isoenzymes in human liver were examined. Rabbit antiserum against porcin soluble (i.e., non-mitochondrial) enzyme cross-reacted with the soluble enzyme of human origin and was used in an immunoprecipitation assay to quantitate the soluble and mitochondrial isoenzymes. These were separated by rapid, semiquantitative electrophoresis on cellulose acetate and by three other quantitative techniques: isoelectric focusing and anion-and cation-exchange chromatography. The mitochrondrial enzyme averaged 81% of the total activity in normal adult human liver (n = 4). Its contribution was dramatically reduced in single specimens of human fetal liver (56% of total activity) and hepatoblastoma tissue (38%). Total enzyme activities (mumol min-1 per gram of tissue) were: adult, 150; fetal, 38; tumor, 6. Total enzyme concentrations (micromoles of enzyme per kilogram of tissue) found were: adult, 10.8; fetal, 2.7; tumor, 0.4. The concentrations and isoenzyme distribution in human liver are compared to those in various animal model systems. Other methods for quantitative estimation of the isoenzymes and their adaptability for use in estimating concentrations in serum are reviewed.