Purification and characterization of wild-type and mutant TK1 type kinases from Caenorhabditis elegans

Caenorhabditis elegans has a single deoxynucleoside kinase-like gene. The sequence is similar to that of human TK1, but besides accepting thymidine as a substrate, the C. elegans TK1 (CeTK1) also phosphorylates deoxyguanosine. In contrast to human TK1, the CeTK1 exclusively exists as a dimer with a molecular mass of approximately 60 kDa, even if incubated with ATP. Incubation with ATP induces a transition into a more active enzyme with a higher kcat but unchanged Km. This activation only occurs at an enzyme concentration in the incubation buffer of 0.5 micro g/ml (8.42 nM) or higher. C-terminal deletion of the enzyme results in lower catalytic efficiency and stability.