Modulation of the catalytic subunit of cyclic AMP-dependent protein kinase by calmodulin, S-100 protein, parvalbumin and troponin.

The activity of the catalytic subunit of cyclic AMP-dependent protein kinase (A-PK), utilizing type II-S, III-S histone or protamine (free base) as a substrate, was augmented in the presence of regulatory protein including calmodulin, S-100 protein, parvalbumin, or troponin. However, inhibition by calmodulin or S-100 but stimulation by parvalbumin or troponin on this A-PK subunit was observed when II-S histone was replaced by V-S, VI-S, VII-S, or VIII-S histone. In addition, the stimulatory effect of calmodulin or S-100 on this A-PK subunit utilizing III-S histone was greatly diminished when half the dose of III-S was replaced by other histones in a bi-mixed form.