Human erythrocyte thiopurine methyltransferase

Radiochemical microassay and biochemical properties

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

Research output: Contribution to journalArticle

259 Citations (Scopus)

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

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thiopurine methyltransferase
Blood
Erythrocytes
Thioguanine
6-Mercaptopurine
Human Activities
Cells
Enzyme Activators
Methionine
Substrates
Kidney
Experiments

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Biochemistry

Cite this

Human erythrocyte thiopurine methyltransferase : Radiochemical microassay and biochemical properties. / Weinshilboum, Richard M; Raymond, F. A.; Pazmiño, P. A.

In: Clinica Chimica Acta, Vol. 85, No. 3, 02.05.1978, p. 323-333.

Research output: Contribution to journalArticle

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