A-Ketovalerate

Thus we designed and synthesized a bicyclic pyridoxamine derivative carrying an oriented catalytic side arm (16) [11], Rates for conversion of the ketimine Schiff base into the aldimine, formed with 26 (below) and a-ketovaleric acid, indolepyruvic acid, or pyruvic acid, were enhanced 20-30 times relative to those carried out in the presence of the corresponding pyridoxamine derivatives without the catalytic side arm. With a-ketovaleric acid, 16 underwent transamination to afford D-norvaline with 90% ee. The formation of tryptophan and alanine from indolepyruvic acid and pyruvic acid, respectively, showed a similar preference. A control compound (17), with a propylthio group at the same stereochemical position as the aminothiol side arm in 16, produced a 1.5 1 excess of L-norvaline, in contrast to the large preference for D-amino acids with 16. Therefore, extremely preferential protonation seems to take place on the si face when the catalytic side arm is present as in 16. 

Ketosis, relation to carbohydrate oxidation, II, 145-159 theory of, II, 146 a-Ketovaleric acids, V, 50 Konigs-Knorr reaction, I, 79, 114 a-glycoside formation in, I, 84 Kojic acid, III, 373 from sucrose, IV, 322, 324... 

D-Amino oxidase is a peroxisomal enzyme that catalyzes the oxidative deamination of D-amino acids to give the corresponding a-keto acids, ammonia, and hydrogen peroxide. In this assay, a-ketovaleric acid from D-valine was quantitated. 

The quinoxalinol derivatives of a-ketovaleric acid and ketovaleric acid (internal standard) were separated on a LiChrospher 100 RP-8 column (4 mm x 250 mm). The mobile phase was a 60 40 ratio of 0.35 Af ammonium acetate and acetonitrile. The eluate was monitored by fluorescence with the excitation and emission wavelengths set at 340 and 420 nm, respectively. 

Maleic acid Oxalic acid Citric acid Pyruvic acid Malonic acid a-Ketobutyric acid a-Ketovaleric acid Succinic acid Glycolic acid Lactic acid Formic acid... 

Only one single concentration term present, and another Michaelis constant equal to zero (B, C, A bAC terms missing). This is an ordered mechanism with addition of A in steady state and B in rapid equilibrium, and examples include glutamate dehydrogenase with a-ketovalerate or a-ketobutyrate as substrates (14). 

DL-Norvaline-3-C on administration to rats or on incubation with rat liver homogenates yielded radioactive a-ketovaleric acid, butyric acid, acetic acid, acetoacetate, and 3-hydroxybutyric acid HI). These compounds were isolated by column cluomatography and their identity established. Degradation of the butyric acid demonstrated that only C-2 was significantly labeled. This established that the butyrate was formed by a direct pathway from norvaline and not by the subsequent condoisation of two-carbon fragments. 

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