D-β-Aminoisobutyrate:pyruvate Aminotransferase in Mammalian Liver and Excretion of β-Aminoisobutyrate by Man

Abstract

Abstract An enzyme which catalyzes a reversible transamination between d-β-aminoisobutyrate and pyruvate was found in the liver of rat, guinea pig, and hog, and the enzyme in an extract of hog liver acetone powder was purified about 200-fold. The enzyme was localized almost exclusively in the liver among the tissues examined in the guinea pig. It was most active against d-β-aminoisobutyrate among the ω-amino acids examined, and had little effect on the l isomer; this specificity is markedly different from that of β-aminoisobutyrate:2-oxoglutarate aminotransferase, for which the d isomer is not a substrate. Since the β-aminoisobutyrate in human urine and liver has the d configuration and a genetically determined high excretor cannot destroy the amino acid, it was postulated that the enzyme activity might be absent from the liver of genetic high excretors of β-aminoisobutyrate. The activity of the enzyme in liver and the concentration of β-aminoisobutyrate in urine were measured in material obtained at autopsy of 15 bodies. The enzyme activity was always found in the liver specimens from eight low excretors and not found in five of seven high excretors. Thus the genetically determined high excretion of β-aminoisobutyrate occurs most probably because of the absence of the aminotransferase from the liver of excretors.