Shigeko Fujimoto

The level of β-alanine aminotransferase activity in regenerating and differentiating rat liver

beta-Alanine aminotransferase from rat liver was purified to electrophoretic homogeneity. The immunological and kinetic properties of this enzyme were similar to those of the enzyme from rat brain. However, the liver enzyme transaminates from beta-alanine to 2-oxoglutaric acid, while the brain enzyme transaminates from gamma-aminobutyric acid. beta-Alanine aminotransferase activity in regenerating rat liver was lower than that in control rat liver. Activity of this enzyme, as well as of other uracil-catabolizing enzymes (Weber, G., Queener, S.F. and Ferdinandus, A. (1970) in Advances in Enzyme Regulation (Weber, G., ed.), Vol. 9, pp. 63-95, Pergamon Press, Oxford), was low in newborn rat liver and increased about 5-fold, reaching the level observed in adult rat liver. beta-Alanine and prednisolone induced beta-alanine aminotransferase in rat liver.

Increased β-aminoisobutyric acid in rat liver with 6-azauracil and its enantiomer

When 6‐azauracil was subcutaneously injected, β‐aminoisobutyric acid and β‐alanine contents were increased 22 and 61‐fold, respectively, in rat liver. Incorporation of [methyl‐14Cithymine into β‐aminoisobutyric acid was increased to 42‐fold by 6‐azauracil treatment. The absolute configuration of this amino acid was proved to be the (R)‐form by means of a gas‐chromatographic technique. 6‐Azauracil inhibited β‐alanine‐pyruvate aminotransferase activity with an I 50 of approx. 2.5 mM.

Identity of β-alanine-oxo-glutarate aminotransferase and L-β-aminoisobutyrate aminotransferase in rat liver

Abstract L -β-Aminoisobutyrate served as an amino donor for purified β-alanine-oxo-glutarate aminotransferase from rat liver when 2-oxoglutarate was employed as an amino acceptor, but he D -isomer did not. L -β-Aminoisobutyrate acted as a competitive inhibitor with respect to β-alanine and had a Ki of approximately 2.6 mM, which is the same value as the Km of 2.7 mM. When the crude extract was applied to a DEAE-Sepharose CL-6B column, L -β-aminoisobutyrate aminotransferase and β-alanine-oxo-glutarate aminotransferase activities were found in the same fractions with a single peak. Antiserum to rat liver β-alanine-oxo-glutarate aminotransferase inhibited L -β-aminoisobutyrate aminotransferase activity in rat liver in the same way as β-alanine-oxo-glutarate aminotransferase activity.

Bisfunction of propionic acid on purified rat liver β-ureidopropionase

Propionic acid and isobutyric acid, which are structural analogues of N‐carbamoyl‐β‐alanine and N‐carbamoyl‐β‐aminoisobutyric acid, respectively, acted as an allosteric activator as well as a competitive inhibitor of purified rat liver β‐ureidopropionase. Propionic acid and isobutyric acid had a K i value of approx. 0.3 mM at pH 7.0. The Hill coefficient for N‐carbamoyl‐β‐alanine was 2.0, but the cooperativity decreased to 1.0 in the presence of 1 mM propionic acid. The K value towards N‐carbamoyl‐β‐alanine was calculated to be 0.17 mM from Hill plots and the K m value was determined to be 0.06 mM from replots of the apparent K m vs propionic acid.

Evaluation of interconversion between (R)- and (S)-enantiomers of β-aminoisobutyrate

Abstract The conversion of (R)- to (S)-β-aminoisobutyrate was observed in the presence of d -3-aminoisobutyrate-pyruvate aminotransferase, aminobutyrate aminotransferase, pyruvate and l -glutamate. The reverse reaction was also found in the presence of 2-oxoglutarate and l -alanine. Neither d -3-aminoisobutyrate-pyruvate aminotransferase nor aminobutyrate aminotransferase revealed a racemase activity of the enantiomorphs.