title: The mechanism of inhibition of Alcaligenes faecalis S-adenosylhomocysteine hydrolase by neplanocin A.
abstract: Neplanocin A, a cyclopentenyl analog of adenosine, has been reported by S. Yaginuma, N. Muto, M. Tsujino, Y. Sudate, M. Hayashi, and M. Otari (1981) J. Antibiot. 34, 359-366 to exhibit antibacterial activity against Alcaligenes faecalis. Since neplanocin A (NpcA) is a known inhibitor of eukaryotic S-adenosylhomocysteine (AdoHcy) hydrolase (EC 3.3.1.1) (R. T. Borchardt, B. T. Keller, and U. Patel-Thombre (1984) J. Biol. Chem. 259, 4353-4358), the present study was undertaken to determine the effects of this carbocyclic nucleoside on AdoHcy hydrolase isolated from a prokaryotic source (A. faecalis). AdoHcy hydrolase was purified to homogeneity by affinity chromatography on an AdoHcy-agarose matrix from A. faecalis. Neplanocin A inactivated the purified AdoHcy hydrolase in a time- and concentration-dependent manner and the enzyme activity could not be recovered by dialysis. The inactivation of this bacterial enzyme by neplanocin A is accompanied by a reduction of three of the six enzyme-bound NAD+s to NADHs. These results suggest that the prokaryotic enzyme, like the eukaryotic AdoHcy hydrolase, is susceptible to inhibition by neplanocin A. The mechanism of inactivation in both cases appears to be a Kcat mechanism involving the reduction of the enzyme-bound NAD+ to NADH. The fact that total inhibition of the prokaryotic AdoHcy hydrolase by NpcA results in a reduction of only three of the six enzyme-bound NAD+s to NADHs suggests that the enzyme shows half-site reactivity (i.e., only three of the six subunits are catalytically active).
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D043383:Adenosylhomocysteinase; D000421:Alcaligenes / Q000201:enzymology*; D001665:Binding Sites / Q000187:drug effects; D006867:Hydrolases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects
chemical_list: D009243:NAD; D009249:NADP; C031096:neplanocin A; D006867:Hydrolases; D043383:Adenosylhomocysteinase; D000241:Adenosine