Inhibition of the catalytic subunit of cAMP-dependent protein kinase by dicyclohexylcarbodiimide.

The hydrophobic carbodiimide dicyclohexylcarbodiimide (DCCD) has been shown to inhibit the catalytic (C) subunit of adenosine cyclic 3',5'-phosphate dependent protein kinase (EC 2.7.1.3) in a time-dependent, irreversible manner. The rate of inactivation was first order and showed saturation kinetics with an apparent Ki of 60 microM. Magnesium adenosine 5'-triphosphate (MgATP) was capable of protecting against this inhibition, whereas neither a synthetic peptide substrate nor histone afforded protection. Mg alone afforded some protection. When the catalytic subunit was aggregated with the regulatory subunit in the holoenzyme complex, no inhibition was observed. The inhibition was enhanced at low pH, suggesting that a carboxylic acid group was the target for interaction with DCCD. On the basis of the protection studies, it is most likely that this carboxylic acid group is associated with the MgATP binding site, perhaps serving as a ligand for the metal. Efforts to identify the site that was modified by DCCD included (1) modification with [14C]DCCD, (2) modification by DCCD in the presence of [3H]aniline, and (3) modification with DCCD and [14C]glycine ethyl ester. In no case was radioactivity incorporated into the protein, suggesting that the irreversible inhibition was due to an intramolecular cross-link between a reactive carboxylic acid group and a nearby amino group. Differential peptide mapping identified a single peptide that was consistently lost as a consequence of DCCD inhibition. This peptide (residues 166-189) contained four carboxylic acid residues as well as an internal Lys.(ABSTRACT TRUNCATED AT 250 WORDS)