... the 5¢-hydroxyl group of thymidine, forming dTMP. Human TK1 is cytosolic and its activity is absent in resting cells, appears in late G1,increases in S phase coinciding with the increase in ... the a-helix dimer interface, and this form is more openthan hTK1. Therefore, at present, it appears that the adenosine group is very loosely bound to hTK1. In the present work, the part of the ... will be in the high- active tetramerform. Recently, phosphorylation of hTK1 at serine 13has been proposed to be involved in this regulation,preventing ATP-induced transformation to the high- active...