Synergism of substrate binding with enzymes, as observed by equilibrium isotope exchange kinetics: model patterns.

The effects of synergistic binding among co-substrates on the kinetic saturation patterns for equilibrium isotope exchange rates have been derived. Models considered for a two reactant-two product system were those in which one substrate may either decrease the dissociation rate or increase the association rate for its co-substrate. These studies help define limits of this versatile kinetic probe technique. The most sensitive indicator for synergistic substrate binding appears to be the different apparent Km values for different exchange rate curves; e.g,, A in equilibrium P and B in equilibrium Q. Model patterns for mutual synergism effects are also presented; the slowest exchange reactions were found the most sensitive to preferred orders of substrate binding. Conditions that can prevent detection of preferred or even compulsory order binding are discussed.