A protein "A" binds to protein "B" to form a complex, AB. A cell contrains an equilibrium mixture of protein "A" at a concentration of 1μM, protein "B" at a concentration of 1μM, and the complex AB also at 1μM.
(A) what is the equilbrium constant, K for the reaction A + B -> AB?
(B) What would the equilbrium constant be if A, B, and AB were each present in equilibrium at a concentration of 1nM?
(C) At this lower concentration, about how many extra hydrogens bonds would be needed to hold A and B together tightly enough to form the same proportion of the AB complex? (Free-energy change is related to the equilibrium constant by the equation ΔG= -2.3 RT log10K, where R is 1.98 x 10-3 kcal/K and T is 310 Kelvin. Assume that the formation of one hydrogen bond is accompanied by a favorable free-energy change of about 1 kcal/mole)