Fox I H, Marchant P J
Can J Biochem. 1976 Dec;54(12):1055-60. doi: 10.1139/o76-154.
The 5'-phosphomonoesterase activity of 5'-nucleotidase (EC 3.1.3.5) and alkaline phosphatase (EC 3.1.3.5) participates in the catabolism of purine ribonucleotides to uric acid in humans. Initial velocity studies of 5'-nucleotidase suggest a sequential mechanism of interaction between AMP nad MgCl2, with a Km of 14 and 3 muM, respectively. With product inhibition studies the apparent Ki's for adenosine, inosine, cytidine, and inorganic phosphate were 0.4, 3.0, 5.0, and 42 mM, respectively. A large number of nucleoside mono-, di-, and tri-phosphate compounds were inhibitors of the enzyme. Allopurinol ribonucleotide, ADP, or ATP were competitive inhititors when AMP was the substrate, with a Ki slope of 120 muM. The phosphomonoesterase activity of human placental microsomal alkaline phosphatase had a pH optimum of 10.0 and had only 18% of maximum activity at pH 7.4. Substrates and inhibitors included almost any phosphorylated compound. The Km for AMP was 0.4 mM and the apparent Ki for Pi was 0.6 mM. Activity was increased only 19% by 5 mM MgCl2. These observations suggest that 5'-nucleotidase and alkaline phosphatase may be inhibited by ATP and Pi, respectively, under normal intracellular conditions, and that AMP may be preferentially hydrolyzed by 5'-nucleotidase.
5'-核苷酸酶（EC 3.1.3.5）和碱性磷酸酶（EC 3.1.3.5）的5'-磷酸单酯酶活性参与人类嘌呤核糖核苷酸分解代谢生成尿酸的过程。对5'-核苷酸酶的初速度研究表明，AMP与MgCl2之间存在顺序相互作用机制，其Km值分别为14 μM和3 μM。通过产物抑制研究发现，腺苷、肌苷、胞苷和无机磷酸的表观Ki值分别为0.4 mM、3.0 mM、5.0 mM和42 mM。大量的核苷单磷酸、二磷酸和三磷酸化合物都是该酶的抑制剂。当以AMP为底物时，别嘌呤醇核糖核苷酸、ADP或ATP是竞争性抑制剂，其Ki斜率为120 μM。人胎盘微粒体碱性磷酸酶的磷酸单酯酶活性在pH 10.0时达到最佳，在pH 7.4时只有最大活性的18%。底物和抑制剂几乎包括任何磷酸化化合物。AMP的Km值为0.4 mM，Pi的表观Ki值为0.6 mM。5 mM MgCl2仅使活性增加19%。这些观察结果表明，在正常细胞内条件下，5'-核苷酸酶和碱性磷酸酶可能分别受到ATP和Pi的抑制，并且AMP可能优先被5'-核苷酸酶水解。
