Alkaline phosphatase activities of 6-thiopurine-sensitive and -resistant sublines of Sarcoma 180
Lee, M.H.; Huang, Y.M.; Sartorelli, A.C.
Cancer Research 38(8): 2413-2418
1978
ISSN/ISBN: 0008-5472 PMID: 27298 Document Number: 126568
The alkaline phosphatase Sarcoma 180/TG to 6-thioguanine and 6-mercaptopurine. Both neoplasms possessed particulate-bound alkaline phosphatase enzymes labeled A and B on the basis of their ease of solubilization from the particulate fraction; more enzyme A was present in both sublines, with the total activity of enzyme fractions A and B being about 100-fold greater in the resistant variant. A storage-labile, sulfhydryl reagent-sensitive factor, presumably a proteolytic enzyme, was involved in the release of alkaline phosphatase A from the particulate fraction of Sarcoma 180/TG. p-Chloromercuribenzoate, iodoacetamide, phenol and ethanol were all potent inhibitors of the solubilization of alkaline phosphatase A from the particulate fraction. Alkaline phosphatases A and B of Sarcoma 180/TG were capable of degrading 6-thioinosine 5'-phosphate to its nucleoside form at optimum and physiological pH values; the rates of hydrolysis of the 6-thioinosine nucleotide were equivalent to those of IMP. Neither enzyme cleaved nucleoside triphosphates such as ATP under the conditions used. Significant differences exist in the properties of these enzymes. The optimum reaction pH of enzymes A and B of Sarcoma 180 were considerably lower than those of the resistant variant and the thermostability and sensitivity of these enzymes to L-homoarginine inhibition differed. The findings, together with reported immunological distinctions, suggest that differences exist between the alkaline phosphatases of Sarcoma 180 and Sarcoma 180/TG.