Abstract
Purine nucleotide degradation in human tissues is highly regulated. Dephosphorylation of nucleoside 5'-monophosphates is the first committed and irreversible reaction of purine nucleotide catabolism. Recent studies indicate that cytoplasmic 5'-nucleotidase may have an important role in intracellular nucleotide degradation. We purified cytoplasmic 5'-nucleotidase from human placenta 8075-fold to a specific activity of 58.85 μmol/ min/mg. The enzyme showed absolute requirement for magnesium with a Km of 6 mM and pH optimum from 7.4 to 9.0. CMP and UMP are preferred substrates. A large variety of purine, pyrimidine and pyridine compounds exert an inhibitory effect on enzyme activity. IMP, GMP and NADH produce almost 100% inhibition at 1.0 mM. Nucleoside di- and triphosphates are potent inhibitors. ATP and ADP are competitive inhibitors with respect to AMP and IMP as substrates with Ki values of 100 μM and 15 μM, respectively. Inorganic phosphate is a noncompetitive inhibitor with Ki values of 19 mM and 43 mM. The estimated molecular weight is 143,000 and the stokes radius is 46.1A. The subunit molecular weight is 76,000, suggesting that the enzyme is a dimeric protein. These data elucidate the nature of cytoplasmic 5'-nucleotidase enzyme and its role in purine nucleotide degradation in human tissues.
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Madrid-Marina, V., Kaminska, J. & Fox, I. HUMAN PLACENTAL CYTOPLASMIC 5′-NUCLEOTIDASE: PURIFICATION AND MOLECULAR PROPERTIES: 115. Pediatr Res 19, 763 (1985). https://doi.org/10.1203/00006450-198507000-00135
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DOI: https://doi.org/10.1203/00006450-198507000-00135