Molecular modeling of manganese regulation of calmodulin-sensitive adenylyl cyclase from mammalian sperm.
The soluble calmodulin-sensitive isoform of adenylyl cyclase isolated from equine sperm is unique because it requires Mn(2+) rather than Mg(2+) for activity. To gain insight into the molecular action of metals on sperm adenylyl cyclase, the kinetics of Mn(2+) and ATP effect was examined. A biphasic response to increases in ATP concentration was observed when metal was held constant. When [Mn(2+)] exceeded [ATP], however, greatly enhanced enzyme activity was observed. The kinetic profiles were consistent with allosteric activation of adenylyl cyclase by Mn(2+). Linear transformation of the data yielded an apparent K(m) for Mn-ATP of 5.8 mM and calculated V(max) of 12 nM cyclic AMP formed/min/mg. Data analysis using calculated equilibrium concentrations of free and complexed reactants provided similar estimates of these kinetic parameters.
Toscano
William A
WA
Division of Environmental and Occupational Health, University of Minnesota School of Public Health, Minneapolis, MN 55455, USA. tosca001@umn.edu
Toscano
John S
JS
Toscano
Diane G
DG
Gross
Mary K
MK
D000255:Adenosine Triphosphate / Q000737:chemistry*; D000262:Adenylyl Cyclases / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D003067:Coenzymes / Q000737:chemistry; D003198:Computer Simulation; D004789:Enzyme Activation; D006736:Horses; D007700:Kinetics; D008297:Male; D008345:Manganese / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D013094:Spermatozoa / Q000737:chemistry* / Q000201:enzymology*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D003067:Coenzymes; D008345:Manganese; D000255:Adenosine Triphosphate; D000262:Adenylyl Cyclases