Human erythrocyte thiopurine methyltransferase: Radiochemical microassay and biochemical properties

R. M. Weinshilboum, F. A. Raymond, P. A. Pazmiño

Research output: Contribution to journalArticle

264 Scopus citations

Abstract

A radiochemical micromethod for the determination of thiopurine methyltransferase (TPMT) activity in human red blood cells (RBC) is described. Both 6-mercaptopurine and 6-thioguanine were substrates for the TPMT activity in the human RBC: Apparent Michaelis-Menten (KM) values for 6-mercaptopurine and 6-thioguanine were 3.2 × 10-4 M and 2.0 × 10-4 M, respectively. The apparent KM value for S-adenosyl-l-methionine, a co-substrate for the reaction, was 1.7 × 10-6 M. The pH optimum for the reaction was approximately 7.5. Blood samples from 73 randomly selected adult subjects had a mean activity of 10.2 ± 2.4 (mean ± S.D.) units/ml packed red blood cells. The range of activities was from 4.6 to 14.2 units/ml. The results of experiments in which partially purified human kidney TPMT was added to RBC lysates and of experiments in which "low" and "high" activity lysates were mixed gave no indication that individual variations in RBC TPMT activity were due to endogenous inhibitors or activators of the enzyme.

Original languageEnglish (US)
Pages (from-to)323-333
Number of pages11
JournalClinica Chimica Acta
Volume85
Issue number3
DOIs
StatePublished - May 2 1978

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Biochemistry
  • Biochemistry, medical

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