ADP and ATP and their analogues were evaluated as inhibitors of 5′-nucleotidase purified from heart plasma membrane. ADP analogues are more powerful inhibitors than the corresponding ATP analogues. The most powerful inhibitor found is adenosine 5′-[alpha beta-methylene]diphosphate (AOPCP) for which the enzyme shows a Ki of 5 nM at pH 7.2. Measurements of pKi values for ADP and AOPCP as a function of pH indicate that the major inhibitory species of both nucleotides is the dianion. In the physiological range of pH values, AOPCP is a more powerful inhibitor than ADP principally because a higher percentage of AOPCP exists in the dianion form. The methylenephosphonate analogue of AMP (ACP), though not a substrate, is a moderately effective inhibitor. The corresponding analogues of ADP (ACPOP) and ATP (ACPOPOP) are as good inhibitors as ADP and ATP respectively. The thiophosphate analogues of ADP all inhibit 5′-nucleotidase, although not as powerfully as ADP, the most effective of these analogues being adenosine 5′-O-(1-thiodiphosphate) diastereoisomer B (ADP[alpha S](B)]. Other nucleotides inhibit the enzyme, but none is as effective as AOPCP. Inorganic tripolyphosphate and methylenediphosphonate are better inhibitors of the enzyme than is inorganic pyrophosphate. Inorganic thiophosphate is a better inhibitor than is orthophosphate. Hill plots of the ADP and AOPCP inhibition yield slopes close to 1; Hill plots of the ATP inhibition yield slopes of about 0.6. MgADP- is not an inhibitor, and MgATP2- is at best a very weak inhibitor of the enzyme.
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Research Article| March 15 1985
5′-Nucleotidase from rat heart membranes. Inhibition by adenine nucleotides and related compounds
Biochem J (1985) 226 (3): 645–651.
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Y Naito, J M Lowenstein; 5′-Nucleotidase from rat heart membranes. Inhibition by adenine nucleotides and related compounds. Biochem J 15 March 1985; 226 (3): 645–651. doi: https://doi.org/10.1042/bj2260645
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