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 a utoinhibitory domain. The molecular bases of this regulation are unkno wn. Their understanding demands functional and structural studies on t he activated purified enzyme. In this paper the plasma membrane H+-ATP ase from maize roots activated in vivo by fusicoccin was solubilised a nd fractionated by anion-exchange HPLC. Results showed that the H+-ATP ase separated from fusicoccin receptors retained fusicoccin activation and that it was more evident after enzyme insertion into liposomes. T hese data suggest that fusicoccin stimulation does not depend on a dir ect action of the fusicoccin receptor on the H+-ATPase, but rather, fu sicoccin brings about a permanent modification of the H+-ATPase which very likely represents a general regulatory mechanism for 'P-type' ATP ases.