Mariko Kikugawa

Analysis of cyclic feed intake in rats fed on a zinc-deficient diet and the level of dihydropyrimidinase (EC 3.5.2.2).

The body weight and feed intake of rats fed on a Zn-deficient diet for 28 d were reduced compared with those of control rats. The feed intakes of the Zn-deficient and control groups during the period were 10.2 (SE 0.3) and 15.7 (SE 0.2) g/d respectively. Cyclic variations in feed intake and body-weight changes were found in analysis not only of all the data for five rats but also that in each individual rat. Cosinor analysis revealed that the cyclical period of both the feed intake and body-weight change in the Zn-deficient rats was 3.5 (SE 0.1) d. The mesor and amplitude value of the feed intake in the Zn-deficient rats was 10.1 (SE 0.4) g/d and 3.5 (SE 0.5) g/d respectively, and that of body-weight change was 1.4 (SE 0.1) g/d and 7.9 (SE 1.3) g/d respectively. Among pyrimidine-catabolizing enzymes, dihydropyrimidinase (EC 3.5.2.2) activity showed significant retardation in the Zn-deficient rat liver with decrease of the enzyme protein. The ratio of apo-form to holo-form dihydropyrimidinase in the liver was not affected by the Zn-deficient diet.

Inhibition of d-3-aminoisobutyrate-pyruvate aminotransferase by 5-fluorouracil and α-fluoro-β-alanine

Among pyrimidine derivatives, we found that 5-fluorouracil;potently inhibited purified rat liver d -3-aminoisobutyrate-pyruvate aminotransferase, whereas 5-fluorouridine did so to a much lesser extent. 5-Fluorouracil acted as a competitive inhibitor against β-alanine with a K i of 56 μM, and was uncompetitive against pyruvic acid, with a K i of 73 μM. α-Fluoro-β-alanine, a metabolite of 5-fluorouracil, was also a competitive inhibitor with respect to β-alanine with a K i of 8.0 mM. 5-Fluorouracil acted also as a competitive inhibitor of 4-aminobutyrate aminotransferase with respect to β-alanine with a K i value of 1.9 mM, and was uncompetitive against 2-oxoglutaric acid, with a K i of 1.8 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.