Human erythrocyte thiol methyltransferase: Radiochemical microassay and biochemical properties

Richard M. Weinshilboum, Susan Sladek, Susanne Klumpp

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


A radiochemical microassay for the measurement of thiol methyltransferase (TMT) activity in human red blood cell (RBC) membranes has been developed. Both 2-mercaptoethanol and dithiothreitol were used as substrates for the enzyme. The pH optimum of the reaction was approximately 9.0 when glycine-NaOH was used as a buffer. The apparent Michaelis-Menten (KM) value for the methyl donor for the reaction, S-adenosyl-l-methionine, was 43 μmol/1. Human RBC TMT activity was neither activated nor inhibited by Ca2+ Mg2+, or tropolone, but the enzyme was inhibited by SKF 525A and by reagents that react with sulfhydryl groups. The mean TMT activity in blood from 289 randomly selected adult white subjects was 10.93 ± 3.22 units per mg protein (mean ± S.D.). The activity was the same in samples from men and women. The results of experiments in which TMT activity was measured in mixtures of RBC membranes with relatively "low" and relatively "high" activities provided no evidence that individual variations in the enzyme activity were due to variations in endogenous TMT activators or inhibitors.

Original languageEnglish (US)
Pages (from-to)59-71
Number of pages13
JournalClinica Chimica Acta
Issue number1
StatePublished - Sep 15 1979

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Biochemistry
  • Biochemistry, medical


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