Methylation of 6-mercaptopurine and 6-thioguanine by thiopurine S-methyltransferase. A comparison of activity in red blood cell samples of 199 blood donors.
OBJECTIVE
To compare 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) as substrates for the methylation reaction catalysed by the enzyme thiopurine S-methyltransferase (TPMT).


METHODS
TPMT activity in haemolysed red blood cells of healthy blood donors was determined twice, using the same experimental setting and equal molar concentrations of 6-TG and 6-MP as substrates. After extraction, the reaction products 6-methyl-TG and 6-methyl-MP were quantified using specific high-performance liquid chromatography procedures.


RESULTS
The medians of the TPMT activities from 199 blood donors were 54.4 nmol 6-MTG g(-1)Hb h(-1) when measured with 6-TG as the substrate and 35.8 nmol 6-MMP g(-1) Hb h(-1) when measured with 6-MP. The correlation coefficient for the 199 pairs of values was 0.8695. On average, TPMT activity was 34% lower with 6-MP as substrate than with 6-TG as substrate.
Kröplin
T
T
Department of Experimental and Clinical Pharmacology and Toxicology, Lübeck Medical University, Germany.
Iven
H
H
D000328:Adult; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D015122:Mercaptopurine; D008745:Methylation; D008780:Methyltransferases / Q000097:blood / Q000378:metabolism*; D013379:Substrate Specificity; D013866:Thioguanine
D015122:Mercaptopurine; D008780:Methyltransferases; C022745:thiopurine methyltransferase; D013866:Thioguanine