Substrate diversity of the cAMP-dependent protein kinase: regulation based upon multiple binding interactions.

The proposition is forwarded that the cAMP-dependent protein kinase is one of quite a small class of enzymes wherein differential modes of binding of its multiple substrates make an important contribution to the end physiological response. It is postulated that a variety of different substrate affinities may have evolved in order to regulate the order of substrate phosphorylation. The recent elucidation of the protein's three-dimensional structure provides the opening to test this as a new concept of cellular regulation.