Guanosine kinase

Combes, A. Lefleuriel, J. Le Floc h, F. The inosine-guanosine kinase activity of mitochondria in tubers of Jerusalem artichoke. Plant Physiol. Biochem., 27, 729-736 (1989)... 

Gaubert, G. Gosselin, G. Boudou, V. Imbach, J.L. Eriksson, S. Maury, G. Low enantioselectivities of human deoxycytidine kinase and human deoxy-guanosine kinase with respect to 2 -deoxyadenosine, 2 -deoxyguanosine and their analogs. Biochimie, 81, 1041-1047 (1999)... 

Studies of purified adenosine kinases have made it clear that inosine and guanosine are not among the substrates of this enzyme, in spite of its broad specificity, and for many years it was not certain whether they were enzymatically phosphorylated or not. Recently, however, LePage and his co-workers 59, 60) have provided data supporting the existence of separate inosine and guanosine kinases in crude extracts of mouse tumors, but these activities have not yet been purified. 

The last essential piece of evidence was the presence of kinases (Figure 4). The levels of adenosine kinase were appreciable in all three extracts. With guanosine and inosine as substrates, the levels of kinase activity were very low or not detectable in the monkey liver and leishmania extracts. However, the level of guanosine kinase activity was high in trichomonas. Inosine kinase activity was also easily detectable in this extract but was considerably lower than that toward guanosine. These enzyme data are clearly consistent with the dominance of the phosphorylase-kinase pathway in trichomonas. 

Of the first class, only one mutant, was obtained, lacking guanosine kinase (<1%), and this mutant is also lov/ered in inosine kinase ( 30% of parent), while adenosine kinase is normal. This result does not clarify, the question, whether the kinases are genetically separable. 

Autoradiography with labeled substrates on cultured fibroblasts has been used to visualize HG-PRT deficiency cells of deficient individuals lack the ability to incorporate hypoxanthine or guanine into nucleic acids, because these purine bases can not be converted to their corresponding mononucleotides (1,2). The alternative pathway to form IMP or GMP via inosine or guanosine is not likely, for, although nucleoside phosphorylase is present, there is no definite evidence for the existence of inosine- or guanosine kinase in human cells (3,4). 

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