Degradation of aspartate aminotransferase in rat liver lysosomes

Highly purified lysosomes from the normal and leupeptin-treated rat livers were subjected to immunoblot analysis using antibodies against cytosolic and mitochondrial isozymes of aspartate aminotransferase (cAspAT and mAspAT). In the case of cAspAT (subunit M.W. = 46K), the leupeptin-treated lysosomes showed a major band of 46K and a minor band of 36K while normal lysosomes showed a major band of 36K and a minor band of 41K. In the case of mAspAT (subunit M.W. = 44K), the leupeptin-treated lysosomes showed a 44K band and the normal lysosomes showed a 40K band. These observations suggest that both cAspAT and mAspAT are sequestered into lysosomes with the original subunit molecular weights and are degraded in the lysosomes by way of sequential formation of relatively stable intermediates with distinct molecular weights.