Formation of an aspartyl phosphate intermediate in the reactions of nucleoside phosphotransferase from carrots.

The nucleoside phosphotransferase from carrots forms N-phosphorylhydroxylamine when substrates are hydrolysed in the presence of hydroxylamine. Denaturation of the enzyme after short incubation with the substrates leads to a protein, in which, after reduction with [3H]NaCNBH3 and complete hydrolysis with 6 M HCl, labelled homoserine can be detected. The first experiment provides evidence for an activated phosphorylenzyme, the second experiment shows that the intermediate is an acyl phosphate formed by a nucleophilic attack of an aspartate beta-carboxylate group.