CLONING OF HUMAN ADENOSINE KINASE CDNA - SEQUENCE SIMILARITY TO MICROBIAL RIBOKINASES AND FRUCTOKINASES

Adenosine kinase catalyzes the phosphorylation of adenosine to AMP and hence is a potentially important regulator of extracellular adenosine concentrations, Despite extensive characterization of the kinetic pro perties of the enzyme, its primary structure has never been elucidated . Full-length cDNA clones encoding catalytically active adenosine kina se were obtained from lymphocyte, placental, and liver cDNA libraries. Corresponding mRNA species of 1.3 and 1.8 kb were noted on Northern b lots of all tissues examined and were attributable to alternative poly adenylylation sites at the 3' end of the gene, The encoding protein co nsists of 345 amino acids with a calculated molecular size of 38.7 kDa and does not contain any sequence similarities to other well-characte rized mammalian nucleoside kinases, setting it apart from this family of structurally and functionally related proteins, In contrast, two re gions were identified with significant sequence identity to microbial ribokinase and fructokinases and a bacterial inosine/guanosine kinase. Thus, adenosine kinase is a structurally distinct mammalian nucleosid e kinase that appears to be akin to sugar kinases of microbial origin.