牛歯髄の Aspartate : 2-Oxoglutarate Aminotransferase Isoenzymes に関する研究

Abstract

Aspartate : 2-oxoglutarate aminotransferase (EC 2. 6. 1. 1) exists as two different isoenzymes in a wide range of animal species, one located in the cytosol, and the other in the mitochondria. The two isoenzymes have been isolated and characterized from mammalian liver, kidney, brain, intestine and heart. However, there is no report on detailed properties of aspartate aminotransferase isoenzymes in animal oral tissues. In the present study, the tissue localization, subcellular distribution and properties of aminotransferase isoenzymes in bovine pulp were examined. 1. The specific activity of the aminotransferase was higher in odontoblastic layer than in central pulp, and higher in coronal pulp than in root pulp, suggesting that the enzyme was mainly located in odontoblasts. 2. Aspartate aminotransferase was presented as two different enzymes in bovine pulp, one located in the cytosol, and the other in the mitochondria. 3. Most of the mitochondrial aminotransferase was suggested to be localized in the mitochondrial inner membrane. 4. The aminotransferase isoenzymes were highly purified and characterized from bovine pulp. The mitochondrial isoenzyme had a molecular weight of approximately 100, 000, an isoelectric point of pH 11 and a pH optimum between 8.5 and 9.0. An apparent Km value was 0.32 mM for L-aspartate and 1.8 mM for 2-oxoglutarate. The enzyme utilized L-aspartate, L-phenylalanine, L-tyrosine and L-tryptophan as amino donor with 2-oxoglutarate as amino acceptor. Other L-amino acids were inactive. The cytosolic isoenzyme had a molecular weight of approximately 100, 000, an isoelectric point of pH 7 and a pH optimum between 8.5 and 9.0. The enzyme was specific for L-aspartate and 2-oxoglutarate. 5. A difference in physical and enzymatic properties was not observed between mitochondrial isoenzymes and between cytosolic isoenzymes in bovine liver and pulp.