Structure-activity relationship of cytoplasmic 5'-nucleotidase substrate sites.
Various 5'-nucleotidases (EC 3.1.3.5) exist in vertebrate tissues. The sequence and cDNA cloning of the membrane-bound ecto-5'-nucleotidase (e-N) and one of the cytosolic isoenzymes, IMP-preferring (c-N-II), but not the cytosolic AMP-preferring form (c-N-I), have been reported. While c-N-II has a broad tissue distribution, c-N-I is found only in vertebrate heart. The published data on substrate specificity involve mainly the naturally occurring nucleoside monophosphates, without a systematic structure-activity relationship study. In the present study we have used a series of AMP and IMP analogues to examine the structure-activity relationship for c-N-I and c-N-II in detail. The rank order of activity of the test compounds differed substantially between c-N-I and c-N-II. c-N-I and c-N-II varied with respect to the following interactions with substrate: (1) hydrogen-bond formation with the substituent in the 6-position of the purine ring (a donor-type with c-N-I and an acceptor-type with c-N-II); and (2) hydrophobic attraction of the 6-position unsubstituted purine ring (more pronounced with c-N-I than with c-N-II). No better substrate than 5'-AMP was found for c-N-I. We propose that c-N-I functions as an AMP-binding protein in the myocardial cell with an important role during ischaemic ATP breakdown when AMP accumulates rapidly.
Skladanowski
A C
AC
Department of Biochemistry, Medical University of Gdansk, Poland.
Hoffmann
C
C
Krass
J
J
Jastorff
B
B
Makarewicz
W
W
D015720:5'-Nucleotidase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D000249:Adenosine Monophosphate / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D003001:Cloning, Molecular; D003600:Cytosol / Q000201:enzymology; D007291:Inosine Monophosphate / Q000378:metabolism; D007527:Isoenzymes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D013329:Structure-Activity Relationship; D014714:Vertebrates
D007527:Isoenzymes; D011994:Recombinant Proteins; D007291:Inosine Monophosphate; D000249:Adenosine Monophosphate; D010744:Phosphoric Monoester Hydrolases; D015720:5'-Nucleotidase