5'-Nucleotidase I from rabbit heart.
5'-Nucleotidase I (N-I) from rabbit heart was purified to homogeneity. After ammonium sulfate precipitation, the purification involved chromatography on phosphocellulose, DEAE-Sepharose, AMP-agarose, and ADP-agarose. The pure enzyme has a specific activity of 318 mumol (mg of protein)-1 min-1. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate yields a subunit molecular weight of 40,000. N-I is activated by ADP but not by ATP, in contrast to the 5'-nucleotidase (N-II) purified by Itoh et al. (1986), which is activated by ATP and, less well, by ADP. N-I displays sigmoidal saturation kinetics in the absence of ADP and hyperbolic kinetics in the presence of ADP. Partially purified N-I was previously shown to prefer AMP over IMP as substrate (Truong et al., 1988); this has been confirmed for pure N-I. Comparison of AMP and ADP concentrations reported to occur in heart with the kinetic behavior of N-I implicates N-I as the enzyme responsible for producing adenosine under conditions leading to a rise in ADP and AMP, such as hypoxia or increased workload. N-I is not activated by the ADP analogue adenosine 5'-methylenediphosphonate (AOPCP) and is only weakly inhibited by relatively high concentrations of AOPCP, in contrast to 5'-nucleotidase from plasma membrane, which is powerfully inhibited by this analogue. N-I shows an absolute dependence on Mg2+ ions. Mn2+ and Co2+ ions can replace Mg2+ ions as activator; Ni2+ and Fe2+ are much less effective, while Ca2+, Ba2+, Zn2+, and Cu2+ fail to activate the enzyme.
Yamazaki
Y
Y
Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02254.
Truong
V L
VL
Lowenstein
J M
JM
D015720:5'-Nucleotidase / Q000302:isolation & purification* / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D007527:Isoenzymes / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009206:Myocardium / Q000201:enzymology*; D011817:Rabbits
D007527:Isoenzymes; D046911:Macromolecular Substances; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D015720:5'-Nucleotidase