The interaction of cations with activity of soluble protein kinase C from mouse brain

The interaction of some cations with the enzymatic activity of soluble protein kinase C was determined in order to elucidate whether protein kinase C can be activated by other metal cations besides Ca2+. Protein kinase C was activated by Ca2+ and Sr2+ having EC50 values of nearly 10 microM and 200 microM, respectively. Ba2+ likewise activated protein kinase C but was less potent. Co2+, Ni2+ and Mn2+ had no activating effects on the activity in the absence of Ca2+, but was slightly reduced in the presence of Ca2+ (0.5 mM). Cations with ionic radii close to Ca2+ (0.99 A) inhibited the activity irrespective of the absence or presence of Ca2+. The order of potency is as follows: Hg2+ greater than Cd2+ approximately Cu2+ much greater than Sm3+ greater than Tb3+ greater than La3+. Pb2+ and Zn2+, which showed a high affinity to SH-groups, as well as Hg2+, Cd2+ and Cu2+, which also inhibited the activity. Thus, among the ions investigated, the alkaline-earth ions Sr2+ and Ba2+ could be substituted for Ca2+, irrespective of ionic radii. The serious environmental pollutants such as Hg2+, Cd2+ or Pb2+ impaired the activity of protein kinase C probably due to SH-blocking.