Biosynthesis of branched-chain amino acids in Schizosaccharomyces pombe: regulatory properties of threonine deaminase

Biosynthetic threonine deaminase (TD) from Schizosaccharomyces pombe has been partially purified from crude extracts by treatment with protamine sulfate, ammonium sulfate precipitation, and gel filtration through Sephadex G-25. In both crude extracts and purified preparations, TD showed marked stimulation by pyridoxal phosphate. A pH optimum for activity was found at pH 9.0, whereas the inhibition caused by the natural feedback inhibitor, l-isoleucine, was maximal at pH 7.4. l-Threonine exhibits homotropic cooperative effects at low pH (7.0-8.0), which are eliminated at pH 9.0, and the affinity for substrate (in terms of K(m)) increased with increasing pH. Enzyme activity could be completely inhibited by isoleucine over a pH range of 7.4 to 9.0; the amount of isoleucine required for 50% inhibition increased with increasing pH. Isoleucine inhibition was pseudocompetitive with respect to substrate and increased the cooperative effects of threonine. l-Valine was found to reverse isoleucine inhibition; it also activated the enzyme in a pH range of 7.0 to 8.0 by eliminating the cooperative effects of threonine, thus normalizing the substrate saturation curves at these pH values. l-Leucine was shown to be a competitive inhibitor with respect to threonine, and to be able partially to reverse isoleucine inhibition. Treatment of TD with mercurials did not result in desensitization to isoleucine inhibition. However, at pH 10, virtually no sensitivity of the enzyme to isoleucine was observed while activity remained strong, which suggests the existence of separate sites on the TD molecule for binding threonine and isoleucine. A tentative model is presented which unifies the kinetic results reported here in terms of the interactions of TD with its effector molecules.

Absolute configuration of a metabolite in the m-fission pathway of protocatechuate

An aldolase, which is induced in Pseudomonas testosteroni during growth with p-hydroxybenzoate, preferentially attacks the R form of 4-hydroxy-4-methyl-2-oxoglutarate, a metabolite of protocatechuate catabolism.

3-Ketoglucose reductase of Agrobacterium tumefaciens

Two kinds of 3-ketoglucose-reducing enzyme were partially purified from the sonic extract of Agrobacterium tumefaciens IAM 1525 grown on a sucrose-containing medium. Both enzymes have a specific requirement for reduced nicotinamide adenine dinucleotide phosphate (NADPH) as a hydrogen donor and catalyze the reduction of 3-ketoglucose to glucose but do not reduce 3-ketoglucosides such as 3-ketosucrose, 3-ketoglucose-1-phosphate, 3-ketotrehalose, and 3-ketocellobiose. From the requirement and substrate specificity of the enzymes, the name NADPH:3-ketoglucose oxidoreductase (trivial name, 3-ketoglucose reductase) was proposed. By diethylaminoethyl-cellulose column chromatography, two reductases were separated, and the early and late eluted enzymes were designated reductase I and II, respectively. K(m) values of reductase I and II were as follows: for 3-ketoglucose both had an identical value of 2.5 x 10(-5)m, and for NADPH the values were 1.0 x 10(-5)m and 1.5 x 10(-5)m, respectively. Optimal pH values were also identical: pH 4.8 to 5.0 in 10(-2)m phosphate buffer. Intracellular localization of the enzymes is discussed.

Partial purification and properties of the pyruvate-uridine diphospho-N-acetylglucosamine transferase from Staphylococcus epidermidis

A method for the partial purification of the pyruvate-uridine-diphospho-N-acetylglucosamine transferase from Staphylococcus epidermidis is presented. Some properties of the enzyme are discussed.

Partial purification and some properties of the uridine diphospho-N-acetylglucosamine-enolpyruvate reductase from Staphylococcus epidermidis

A method for the partial purification of the uridine diphospho-N-acetylglucosamine-enolpyruvate reductase from Staphylococcus epidermidis is presented. Some properties of the enzyme, including its dependence on monovalent cation and flavine adenine dinucleotide, are discussed.