EFFECTS OF PLATELET-ACTIVATING-FACTOR, SPHINGOSINE, AND HEPARIN ON SOME PHOSPHOHYDROLASE AND TRANSPORT ACTIVITIES OF YEAST VACUOLES

The effects of some protein kinase effecters on phosphohydrolase and t ransport activities of yeast vacuoles have been investigated. Platelet -activating factor (PAF), which activates plant vacuolar protein kinas e C, exerted protonophoric and membrane-damaging effects on yeast vacu oles and inhibited ATP-dependent Delta mu(H)+ formation and secondary transport, but stimulated ATPase and pyrophosphatase activities by lif ting proton control. PAF also stimulated pyrophosphatase, polyphosphat ase, and alkaline phosphatase activities in intact vacuoles by increas ing tonoplast permeability for the respective substrates. The lysolipi d sphingosine, an inhibitor of plant vacuolar protein kinase C, slight ly stimulated ATPase activity and ATP-dependent membrane potential gen eration and stimulated pyrophosphatase activity by 200% in yeast vacuo les. The activities of polyphosphatase, alkaline phosphatase, and alph a-mannosidase were not affected by sphingosine, while ATP-dependent ci trate transport was slightly inhibited. Heparin, a casein kinase inhib itor, suppressed ATPase and polyphosphatase activities of intact vacuo les. The polyphosphatase activities of the vacuolar sap and Zwittergen t TM-314-solubilized tonoplast were also inhibited by heparin, in cont rast to the ATPase activity, which was inhibited only in intact vacuol es. Heparin inhibition of polyphosphatase presumably results from thei r direct interaction.