Induced interchain disulfide bonding in cAMP-dependent protein kinase II

Cupric phenanthroline was used to catalyze the formation of disulfide bonds in cAMP-dependent protein kinase II. Incubation of holoenzyme alone with cupric phenanthroline resulted in no disulfide bond formation. In contrast, when holoenzyme was preincubated with cAMP prior to treatment with cupric phenanthroline, specific interchain disulfide bonding was found between the regulatory (R) and catalytic (C) subunits. Formation of the R-C dimer was independent of the phosphorylation state of R. Experiments with R that had been freed of bound cyclic nucleotide suggest that a ternary complex of R, C, and cAMP is necessary for the formation of this cross-linked species. When the dimeric R-subunit alone was incubated with cupric phenanthroline, the two protomers of the R-dimer were frequently cross-linked. Phosphorylation of R did not affect the formation of R-R dimers. In contrast to the R-subunit of the type I protein kinase, R-R dimers of the type II protein kinase were not normally observed in the absence of an added catalyst. Factors which favor disulfide bond formation in the R-dimer have not been determined.