Modulators of rat liver cytosol casein kinases 1 and 2

Rat liver cytosol casein kinases 1 and 2 are similarly activated by spermine and inhibited by caffeine. On the contrary they are differently affected by heparin and basic proteins. Low concentrations of heparin inhibited selectively the phosphorylation of casein by casein kinase 2 whereas protamine and histones inhibited specifically casein kinase 1. On the contrary the basic proteins stimulated slightly the activity of casein kinase 2 and released its inhibition by heparin. Increasing the concentration of casein substrate reversed both the inhibition of casein kinase 1 by protamine as well as that of casein kinase 2 by heparin. The data suggest the existence of modulators having either similar or opposite effects on each type of casein kinase.