5'-Deoxy-5'-methylthioadenosine (MTA) phosphorylase was purified 13.4-fold from human peripheral lymphocytes. The enzyme demonstrated normal Michaelis-Menten kinetics with Km values of 26 μM and 7.5 mM for the two substrates. MTA and phosphate, respectively. The rate of MTA degradation was temperature dependent, 47° being the optimum temperature. Five structural analogs served as alternative substrates with Km values ranging from 31 to 53 μM while two compounds, 5'-deoxy-5'methylthiotubercidin (MTT) (Ki = 31 μM) and adenine (Ki = 172 μM), were inhibitory. These same analogs were examined as inhibitors of mitogen-induced human lymphocyte blastogenesis. MTT was found to be the most effective inhibitor of lymphocyte transformation with an I50 of 80 μM.
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