The biochemical genetics of human gamma-aminobutyric acid transaminase.

1. Two methods have been devised for the detection after electrophoresis of gamma-aminobutyric acid transaminase (GABAT) isozymes. 2. GABAT isozymes can be detected in liver, brain, kidney, pancreas, heart, testis. spinal cord and upper jejunum. The greatest activity occurs in liver. 3. Three different commonly occurring electrophoretic types of GABAT have been identified. It seems likely that they are determined by two alleles at an autosomal locus (GABAT). 4. The gene frequencies of GABAT1 and GABAT2 in a random sample of European livers were 0.56 and 0.44 respectively. 5. The three banded patterns seen in heterozygotes suggest that GABAT is a dimeric enzyme. 6. GABA, beta-alanine and 5-aminovaleric acid can act as substrates for GABAT. 7. GABAT activity can be demonstrated in all areas of human brain with the exception of the corpus callosum. Brain samples from patients with Huntington's chorea show no abnormal GABAT activity or unusual phenotypes.