BRAIN PROTEIN AND ITS EFFECT ON CA2+- AND PROTEIN MODULATOR-ACTIVATED CYCLIC NUCLEOTIDE PHOSPHODIESTERASE

Bovine brain cyclic nucleotide phosphodiesterase was found to require higher concentrations of the Ca2+-regulated protein modulator for activation than the heart enzyme. This was due to the presence of an inhibitory factor in brain preparations. The factor could be separated from the enzyme by gel filtration on a G-200 Sephadex column. Rechromatography of the factor on a G-200 Sephadex column showed a single activity peak with an estimated MW of 110,000. The factor appears to be a protein since it was susceptible to trypsin or chymotrypsin but not to RNase, DNase or amylase. The protein factor specifically counteracts the activation of phosphodiesterase by the protein modulator. This protein factor may be either a new regulator for phosphodiesterase or an additional modulator-regulated enzyme.