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Human thiopurine methyltransferase: no evidence of activation by its substrates
I Stupans1, A Kirlich, R A McKinnon
1Centre for Pharmaceutical Research, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide. ieva.stupans@unisa.edu.au
Life Sciences
|February 5, 1998
Abstract:
A HPLC assay was developed to assay baculovirus expressed human thiopurine methyltransferase activity. Using 6-mercaptopurine as substrate, the expressed thiopurine methyltransferase was found to have an apparent Km of 0.99 mM and a Vmax of 19 nmoles/mg/min. These values are in agreement with those determined using the standard radiometric assay for thiopurine methyltransferase activity. The effects of 6-thioguanine on 6-mercaptopurine metabolism were determined. 6-Thioguanine was found to be a mixed inhibitor of 6-mercaptopurine methylation.