The distribution and isozyme patterns of branched chain amino acid aminotransferase(BC AT, EC 2.6. 1. 42) in normal rabbit skim tissues and papilloma tissues have been studied. The activity of branched chain amino acid aminotransfe rase was measured by the method of Ichihara and Koyama(1966). Isozyme patterns of this enzyme was also examined by using DEAE´ cellulose column chromatography. The results obtained were as follows.
1. The activity of the BCAT in normal rabbit skin tissues and papilloma tissues was found to be 109.53 units and 135.35 units per g of wet tissue, respectively. The activity of this enzyme was relatively low compared with that in rat tissues and tumor cells, i.e., liver, heart, pancreas, hepatoma.
2. The distribution of the BCAT in normal rabbit skin tissue showed that 80.29% of the activity was in cytosolic fraction, 13.76,,o in mitochondrial fraction and 5.95% in nuclear fraction.
3. The distribution of the BCAT in papilloma tissues indicated that 83.61% of the activity was in cytosolic, 10. 61 % in mitochondrial and 5.78% in nuclear fraction.
4. Leucine was the most sensitive substrate among the three branched chain amino acids for the BCAT in normal rabbit skin, whereas valine was the best substrate for the BCAT in papilloma tissues.
5. Cytosolic fraction of normal rabbit skin tissue and papilloma tissue contained isozyme I and Z, but not isozyme I, of the BCAT. Isozyme I and M were catalyzed the transaminatien of all three branched chain amino acids.
6. Normal rabbit skin tissue contained isozyme I and ff[ of the BCAT. The relative amounts of the above two isozymes were 71.14% and 28.86%, respectively. Tile relative activity of isozyme I and 3 in papilloma tissue was 57.52% and 42.48%%, respectively.
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