Demonstration of an altered S-adenosylmethionine synthetase in human malignant tumors xenografted into athymic nude mice.
S-Adenosylmethionine synthetase isoenzymes (EC 2.5.1.6) were studied in human malignant tumors xenografted into athymic nude mice and were studied in normal human and rat tissues. The tumors included 7 melanomas; 4 colon carcinomas; 3 each of mammary, cervical, and ovary carcinomas; 2 each of lung carcinomas and sarcomas; and 1 each of lymphoma and stomach and nasopharyngeal carcinomas. The presence of an altered intermediate Michaelis constant (Km) isoenzyme, previously shown to be a unique characteristic of rat neoplastic tissues, in these tumors was invariably detectable, though the presence of the low-Km isoenzyme characteristic of the enzyme of normal tissues was also evident in many of these tumors. Only tumors demonstrating high rates of growth were devoid of the low-Km isoenzyme. The low-Km isoenzyme was the only enzyme detectable in many normal human and rat tissues. Thus this isoenzyme was probably the common enzyme of all tissues. Some additional organ-specific isoenzymes were found, e.g., in the liver and lactating mammary gland. The low-Km isoenzyme in malignant tumors was altered to assume a considerably higher Km value, and this alteration appeared to be a common aberration of malignant tumors.
D000818:Animals; D006801:Humans; D007527:Isoenzymes / Q000032:analysis*; D007700:Kinetics; D008716:Methionine Adenosyltransferase / Q000032:analysis*; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000032:analysis / Q000201:enzymology*; D009374:Neoplasms, Experimental / Q000201:enzymology; D051381:Rats; D014018:Tissue Distribution; D014166:Transferases / Q000032:analysis*; D014183:Transplantation, Heterologous
D007527:Isoenzymes; D014166:Transferases; D008716:Methionine Adenosyltransferase