Mechanism of the reaction catalyzed by staphylococcal nuclease: identification of the rate-determining step.

The hydrolysis of single-stranded DNA catalyzed by wild-type staphylococcal nuclease (SNase) and two mutants has been studied as a function of both pH and solvent viscosity. The κ cat for wild-type SNase increases with pH; the slope of the plot of log k cat vs pH=0.45±0.01. The dependence of k cat /K m on pH for wild-type SNase is biphasic with a break at pH ∼8: for pH ≤8, the plot of log k cat vs pH is linear with a slope=1.20±0.06; for pH ≥8, the slope=0.00±0,04