PURIFICATION AND CHARACTERIZATION OF THE CATALYTIC SUBUNIT OF CAMP-DEPENDENT PROTEIN-KINASE FROM THE BIVALVE MOLLUSK MYTILUS-GALLOPROVINCIALIS

The catalytic subunit of cyclic AMP-dependent protein kinase was isolated from mantle tissue of the sea mussel Mytilus galloprovincialis and purified to apparent homogeneity using a simple two-step procedure. The purified enzyme had a molecular weight of 40 +/- 1.5 kDa on electrophoresis under denaturing conditions, Stokes' radius 25.8 Angstrom and isoelectric point (pI) 8.5. Kinetic experiments showed that the mussel enzyme used Mg2+ as preferred divalent cation (it was inactive in the presence of Mn2+) and the apparent K-m values for MgATP and histone II-A were 43 +/- 7 mu M and 1.72 +/- 0.65 mg/ml, respectively, Mussel C-subunit was inhibited by the regulatory subunit (type RII) of cAMP-dependent protein kinase from mammals and also by the inhibitor peptide PKI(5-24) with a I-50 of 6.5 +/- 1.6 nM. When RII-subunit from porcine heart was incubated, in the presence of [gamma-P-32]ATP, with C-subunit from mussel or porcine, a comparable rate of regulatory subunit phosphorylation was achieved, These physical and biochemical properties lead to the conclusion that the catalytic subunit of cAMP-dependent protein kinase from a bivalve mollusc is closely related to its counterparts from mammalian sources.