[The effect of PAF, sphingosine and heparin on certain phosphohydrolase and transport activity of yeast vacuoles].

The effects of some protein kinase effectors on phosphohydrolase and transport activities of yeast vacuoles have been studied. The platelet-activating factor (PAF), a plant vacuolar protein kinase C stimulator, had a protonophoric and membrane-damaging effects on yeast vacuoles and inhibited the ATP-dependent delta mu H+ formation and ATP-dependent secondary transport but stimulated the ATPase and pyrophosphatase hydrolase activities by abrogating proton control. PAF increasing the tonoplast permeability for the corresponding substrates also stimulated pyrophosphatase, polyphosphatase and alkaline phosphatase activities. Lysolipid sphingosine, a plant vacuolar protein kinase C inhibitor, poorly stimulated the ATPase activity and the ATP-dependent formation of Em in isolated yeast vacuoles, while the pyrophosphatase activity increased by 200%. Other hydrolase activities tested were insensitive to the effect of the lysolipid. Sphingosine inhibited the ATP-dependent citrate transport only insignificantly. Heparin, an effective casein kinase inhibitor, suppressed the ATPase and polyphosphatase activities in isolated yeast vacuoles. The polyphosphatase activity was inhibited both in the vacuolar sap and the tonoplast solubilized by a Zwittergent TM-314, in contrast with the ATPase activity which was inhibited by heparin only in isolated vacuoles. Heparin is suggested to inhibit polyphosphatase by directly influencing the enzyme.