Inability of parvalbumin to function as a calcium-dependent activator of cyclic nucleotide phosphodiesterase activity

The calcium-sensitive phosphodiesterase-stimulating activity sometimes associated with parvalbumin preparations is due to contaminating (less than 0.1%) amounts of carp muscle CDR (calcium-dependent regulator)-like protein. This protein can be resolved from parvalbumins by Sephadex G-75 chromatography and has many characteristics of the CDR. Parvalbumin itself causes a nonspecific stimulation of phosphodiesterase at all calcium concentrations which, in the presence of CDR, can cause an apparent shift to a lower concentration of the calcium level required for half-maximal stimulation.