Multiprotein complexes are formed by weak noncovalent interactions between the proteins. Suppose proteins A and B form a heterodimer with a K_d = 10^-6 M:

(a) Calculate the fraction of monomers that exist in the heterodimer complex if the total concentration of A + B inside the cell is 5μM. Assume [A]_total = [B]_total. 

(b) If the cell is now disrupted in buffer, the cell contents are diluted 5-fold. What fraction of monomers would exist in the complex under these conditions? 

(c) What does this calculation tell you about detecting multiprotein complexes in cell-free homogenates? Should they be readily detectable? If not, what methods might you use to aid in their detection?

Transcribed Image Text:

AB A + B Ka = [A] [B] [AB] = 10 M