FORMATION OF PURINE AND PYRIMIDINE NUCLEOSIDES, DEOXYNUCLEOSIDES, AND THE CORRESPONDING MONONUCLEOTIDES BY SALMON MILT EXTRACT NUCLEOSIDE PHOSPHORYLASE AND NUCLEOSIDE KINASE ENZYMES

A cell-free extract of immature Salmo gairdneri milts possessed both nucleoside and deoxynucleoside phosphorylase activities. Formation of guanosine, deoxyguanosine, uridine, deoxyuridine, thymidine, thymine riboside, inosine, and deoxycytidine from the corresponding purine or pyrimidine bases was very marked, and the formation of deoxyinosine and cytidine generally was less pronounced, under the experimental conditions. The extract also possessed nucleoside phosphokinase and deoxynucleoside phosphokinase activities, although these were considerably less marked than the former. Formation of the mononucleotides of adenosine, uridine, thymidine, deoxyuridine, guanosine, inosine, and deoxyinosine in the presence of adenosinetriphosphate was recorded. When orotic acid was employed as enzyme substrate, uridine, deoxyuridine, and uridylic acid were formed. Comparatively feeble formation of cytidylic and deoxycytidylic acids from the corresponding nucleosides was found. The possible significance of these findings, in relation to known routes of biosynthesis of mononucleotides, is discussed.