The H⁺-ATPase purified from maize root plasma membranes retains fusicoccin in vivo activation

The activity of 'P-type' ATPases is modulated through the C-terminal autoinhibitory domain. The molecular bases of this regulation are unknown. Their understanding demands functional and structural studies on the activated purified enzyme. In this paper the plasma membrane H⁺-ATPase from maize roots activated in vivo by fusicoccin was solubilised and fractionated by anion-exchange HPLC. Results showed that the H⁺-ATPase separated from fusicoccin receptors retained fusicoccin activation and that it was more evident after enzyme insertion into liposomes. These data suggest that fusicoccin stimulation does not depend on a direct action of the fusicoccin receptor on the H⁺-ATPase, but rather, fusicoccin brings about a permanent modification of the H⁺-ATPase which very likely represents a general regulatory mechanism for 'P-type' ATPases.