Specificity in the assembly of multisubunit proteins.

The recoveries of activity in the presence of mixtures of several enzymes and a cellular debris were compared with the recoveries of the pure enzymes. In the acid-dissociation experiments, no interference from foreign proteins was observed nor were any cross hybrids between subunits of different enzymes found. This suggests that the intersubunit binding sites are highly specific and have been selected over evolutionary time for correct assembly. In the urea experiments, cross hybridization and decreased yields were observed in a few cases but in most cases the "foreign" unfolded chains did not influence the recovery of the test enzyme. The results suggest that compartmentalization, temporal or spatial, will not be required as far as assembly of subunits of cytoplasmic enzymes is concerned. The results suggest some cross reaction might occur if all peptide chains were unfolding together. If folding occurs during or immediately after translation, this difficulty would be avoided.