Polyamines and basic proteins stimulate activation by cAMP and catalytic activity Mucor rouxii

Partial activation of Mucor rouxii cAMP-dependent protein kinase by cAMP was obtained when kemptide was used as substrate, but complete activation was attained with cAMP plus protamine or histone. Full activation could not be achieved by increasing kemptide or cAMP concentration. Complete activation by cAMP could be obtained by addition of 10 μM polylysine, 10 μM lysine-rich histone or 0.5 mM spermine plus spermidine. The degree of stimulation could be up to 5-fold, depending on the amount of enzyme in the assay. The same concentrations of polycations increased 1.5-2.3-fold the V_max of kemptide phosphorylation by the free catalytic subunits of both Mucor and bovine heart protein kinases; 10 μM polyarginine inhibited completely the activity of both enzymes.