Development of an improved assay for purine nucleoside kinase activity in cell extracts and detection of inosine kinase activity in Brevibacterium acetylicum ATCC 953, related species, and Corynebacterium flaccumfaciens ATCC6887

An improved assay was developed to detect direct purine nucleoside phosphor ylating activity in cell-free extracts. Direct inosine phosphorylating acti vity was detected in 2 of 70 species tested. Both activities, which depende d on magnesium ion and ATP, phosphorylated a hydroxyl group at the 5' posit ion of inosine. The new assay was shown to be useful for screening of direc t purine nucleoside phosphorylating activity and have the potential to dete ct inosine kinase in the presence of a background of nucleoside phosphoryla se and purine phosphoribosyltransferase activities. Previously, the latter two activities made it difficult to correctly detect direct phosphorylation of inosine by inosine kinase.