Tetrose metabolism. 1. The preparation and degradation of specifically labelled [14C]tetroses and [14C]tetritols

Abstract

The following preparations are described: (a) hydroxy[3-Cl4]pyruvate and L-[3-Cl4]serine from DL-[3-Cl4]serine by D-amino acid oxidase; (b) [2-C14]glycolaldehyde from [3-Cl4]serine by decarboxylation with ninhydrin; (c) L-[l-Cl4]-erythrulose and L-[4-C14]erythrulose from the action of transketolase on the appropriately Cl14-labelled hydroxy-pyruvate and glycolaldehyde; (d) L-[4-C114]erythrulose by the action of crude muscle aldolase on a mixture of H. C14 HO and dihydroxyacetone phosphate, followed by phosphatase hydrolysis of the erythrulose 1-phosphate so formed ( it is shown enzymically that this compound is the L-isomer of erythrulose); (e) L-[l-Cl4]-erythrulose similarly, by aldolase action on unlabelled formaldehyde and [1-C14dihydroxy-acetone phosphate, prepared enzymically from D-[1-Cl4]glucose. L-[l-C14] Threitol was prepared enzymically from either L-[l-C14] erythrulose or L-[4-C14]erythrulose, by means of reduced triphos-phopyridine nucleotide and the "diphosphopyridine nucleotide-xylitol (D-xylulose) dehydrogenase" of guinea pig liver. The isotopic identity of L-[1-Cl4]threitol and L-[4-C14]threitol is experimentally proved, in confirmation of theoretical prediction. The correspondingly labelled erythritols are expected to be different compounds, but this remains to be investigated. The preparation of D-[4-C14]erythrose by periodate oxidation of D-[6-C14]glucose is described. By hydrogena-tion of the above-mentioned tetroses corresponding tetritols were prepared. The position of isotopic labelling in the tetroses and tetritols has been determined by a study of the products of periodate oxidation of the free tetritols or of the phenylosazone of erythrulose (or erythrose). The substrate specificity of the "triphosphopyridine nucleotide-xylitol (L-xylulose) dehydrogenase" of guinea pig liver has been shown to include D-threitol, as well as xylitol, for which substrate this enzyme was previously regarded as completely specific.