Purification and properties of branched chain amino acid aminotransferase from Fasciola hepatica

ABSTRACT

The distribution and properties of branched chain amino acid aminotransferase(EC 2.6.1.42) was investigated in adult Fasciola hepatica. Fasciola hepatica was fractionated by differential centrifugation into nuclear, mitochondrial and cytosolic fractions. The activity of branched chain amino acid aminotransferase was measured by the method of Ichihara and Koyama (1966) . Isozyme patterns of this enzyme was also examined by DEAE-cellulose column chromatography. The results obtained were as follows The activity in homogenate was found to be 12.69 units/g wet tissue. The activity of this enzyme was relatively high compared with those in rat tissues. The distribution of branched chain amino acid aminotransferase in the subcellular organelles showed that 87.8 percent of the activity was in cytosolic, 10.9 percent in mitochondrial and 1.3 percent was in nuclear fraction. Cytosolic fraction of Fasciola hepatica contained Enzyme I, but not Enzyme II and III, of branched chain amino acid aminotransferase. Enzyme I was eluted by 50 mM phosphate buffer from DEAE-cellulose column and catalyzed the transamination of all three branched chain amino acids. The Enzyme I was purified about 22-folds increase in specific activity after chromatography on DEAE-cellulose. The best substrate among three amino acids (leucine, isoleucine and valine) was L-isoleucine. The optimal temperature of Enzyme I was 45 C and the optimal pH was 8.2. The Km value for leucine of Enzyme I was 4.17 mM. The Km values for alpha-ketoglutarate and pyridoxal phosphate of Enzyme I were 0.41 mM and 4.76 x 10(-3) mM, respectively.