Guanosine kinase from Trichomonas vaginalis.

A novel guanosine kinase was partially purified from the parasitic protozoan Trichomonas vaginalis. Unlike nucleoside kinases from other sources, the preferred substrate for this enzyme was guanosine (Vmax/Km = 120). The enzyme also catalyzed the phosphorylation of inosine (Vmax/Km = 3), uridine (2), adenosine (0.5), cytidine (0.2), and 2'-deoxyguanosine (0.1). The 2'-deoxyribonucleosides of adenine, hypoxanthine, uracil, cytosine and thymine were not phosphorylated. The Km for ATP was 6.6 microM. The enzyme was extremely labile in the absence of ATP. As a result, only a 20-fold purification with 25% recovery of activity was possible. However, this preparation was free of nucleoside phosphorylase, nucleoside phosphotransferase and the distinct uridine kinase. The enzyme had a broad optimum of pH 6.5-8. It had a molecular weight of 15000.