Abstract
The soluble calmodulin-sensitive isoform of adenylyl cyclase isolated from equine sperm is unique because it requires Mn2+ rather than Mg 2+ for activity. To gain insight into the molecular action of metals on sperm adenylyl cyclase, the kinetics of Mn2+ and ATP effect was examined. A biphasic response to increases in ATP concentration was observed when metal was held constant. When [Mn2+] exceeded [ATP], however, greatly enhanced enzyme activity was observed. The kinetic profiles were consistent with allosteric activation of adenylyl cyclase by Mn2+. Linear transformation of the data yielded an apparent Km for Mn-ATP of 5.8mM and calculated Vmax of 12nmol cyclic AMP formed/min/mg. Data analysis using calculated equilibrium concentrations of free and complexed reactants provided similar estimates of these kinetic parameters.
Original language | English (US) |
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Pages (from-to) | 91-96 |
Number of pages | 6 |
Journal | Biochemical and Biophysical Research Communications |
Volume | 312 |
Issue number | 1 |
DOIs | |
State | Published - Dec 5 2003 |
Bibliographical note
Funding Information:Supported in part by a grant from NIH: ES-07155.
Keywords
- Allostery
- Cyclic nucleotides
- Fertility
- Kinetics
- Metal ions
- Molecular modeling
- Signal transduction
- Sperm motility