TY - JOUR
T1 - Human erythrocyte thiopurine methyltransferase
T2 - Radiochemical microassay and biochemical properties
AU - Weinshilboum, R. M.
AU - Raymond, F. A.
AU - Pazmiño, P. A.
PY - 1978/5/2
Y1 - 1978/5/2
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=0017880983&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0017880983&partnerID=8YFLogxK
U2 - 10.1016/0009-8981(78)90311-X
DO - 10.1016/0009-8981(78)90311-X
M3 - Article
C2 - 657528
AN - SCOPUS:0017880983
SN - 0009-8981
VL - 85
SP - 323
EP - 333
JO - Clinica Chimica Acta
JF - Clinica Chimica Acta
IS - 3
ER -