Deoxynucleoside kinases of Giardia intestinalis

Giardia intestinalis lacks the ability to synthesise deoxyribonucleotides de novo and must rely on salvage synthesis. Two separate kinases, specific for purines (deoxyadenosine and deoxyguanosine) and pyrimidines (thymidine and deoxycytidine), respectively, are responsible for the incorporation of deoxyribonucleosides. A substantial degree of purification was achieved for the purine deoxynucleoside kinase by the combination of Mono Q anion exchange chromatography, preparative gel electrophoresis and Superose 12 gel filtration. An overall recovery of 4%, with 186- and 174-fold purification, for deoxyguanosine kinase and deoxyadenosine kinase activities, respectively, was observed. The molecular weight was found to be approximately 80000 by gel filtration. Only a partial purification of thymidine/deoxycytidine kinase was achieved. However, both pyrimidine activities remained associated throughout various purification procedures and appeared to be associated with a protein of 44 kDa.