TY - JOUR
T1 - Human erythrocyte phenol O-methyltransferase
T2 - Radiochemical microassay and biochemical properties
AU - Pazmiño, P. A.
AU - Weinshilboum, R. M.
N1 - Funding Information:
This study was supported in part by NIH grants NS 11014 and HL 17487. Dr. Weinshilboum is an Established Investigator of the American Heart Association. We thank Fredrick Raymond, Joel Dunnette and Luanne Wussow for their assistancew ith these studies. We also thank Drs. J.C. Mitchell, P. Frohnert and V. Torres for providing blood samplesf rom patients.
PY - 1978/10/16
Y1 - 1978/10/16
N2 - A radiochemical microassay for the determination of phenol O-methyltransferase (PMT) activity in human red blood cell membranes has been developed. Acetaminophen was used as the substrate. The apparent Michaelis-Menten (KM) value for acetaminophen was 21.2 × 10-3 M. The apparent KM value for S-adenosyl-L-methionine, a co-substrate for the reaction, was 4.8 × 10-6M, and the pH optimum of the reaction was approximately 9.0 with four different buffer systems. Phenol was also tested as a substrate and had an apparent Km value of 2.0 × 10-3 M. Human erythrocyte (RBC) membrane PMT activity did not have the biochemical characteristics of catechol O-methyltransferase, another RBC membrane methyltransferase enzyme activity. Blood samples obtained from 212 randomly selected adult white subjects had a mean activity of 134.5 ± 41.5 pmol of p-acetanisidide formed per mg protein per hour (mean ± S.D.). Activities varied from 44 to 282 units. There were no differences in the mean activities of samples from men and women. Experiments in which mixtures of "low" and "high" activity RBC membrane preparations were assayed for PMT provided no evidence that the variations in enzyme activity were due to the presence of endogenous PMT activators or inhibitors. RBC membrane PMT activity in blood from 9 patients with renal failure, a pathological state in which there are elevated circulating levels of phenols, was found to be significantly decreased with average activity of 76.2 ± 9.7 (mean ± S.E.M., P < 0.001).
AB - A radiochemical microassay for the determination of phenol O-methyltransferase (PMT) activity in human red blood cell membranes has been developed. Acetaminophen was used as the substrate. The apparent Michaelis-Menten (KM) value for acetaminophen was 21.2 × 10-3 M. The apparent KM value for S-adenosyl-L-methionine, a co-substrate for the reaction, was 4.8 × 10-6M, and the pH optimum of the reaction was approximately 9.0 with four different buffer systems. Phenol was also tested as a substrate and had an apparent Km value of 2.0 × 10-3 M. Human erythrocyte (RBC) membrane PMT activity did not have the biochemical characteristics of catechol O-methyltransferase, another RBC membrane methyltransferase enzyme activity. Blood samples obtained from 212 randomly selected adult white subjects had a mean activity of 134.5 ± 41.5 pmol of p-acetanisidide formed per mg protein per hour (mean ± S.D.). Activities varied from 44 to 282 units. There were no differences in the mean activities of samples from men and women. Experiments in which mixtures of "low" and "high" activity RBC membrane preparations were assayed for PMT provided no evidence that the variations in enzyme activity were due to the presence of endogenous PMT activators or inhibitors. RBC membrane PMT activity in blood from 9 patients with renal failure, a pathological state in which there are elevated circulating levels of phenols, was found to be significantly decreased with average activity of 76.2 ± 9.7 (mean ± S.E.M., P < 0.001).
UR - http://www.scopus.com/inward/record.url?scp=0018122252&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0018122252&partnerID=8YFLogxK
U2 - 10.1016/0009-8981(78)90331-5
DO - 10.1016/0009-8981(78)90331-5
M3 - Article
C2 - 709878
AN - SCOPUS:0018122252
SN - 0009-8981
VL - 89
SP - 317
EP - 329
JO - Clinica Chimica Acta
JF - Clinica Chimica Acta
IS - 2
ER -