The lysolipid sphingosine modulates pyrophosphatase activity in tonoplast vesicles and isolated vacuoles from a heterotrophic cell suspension culture of Chenopodium rubrum

The proton pumping activity of the tonoplast (vacuolar membrane) H+‐ATPase and H+‐pyrophosphatase (H+‐PPase) has been studied on a tonoplast‐enriched microsomal fraction and on intact vacuoles isolated from a heterotrophic cell suspension culture of Chenopodium rubrum L. in the presence of the lysosphingolipids D‐sphingosine, psychosine (galactosylsphingosine) and lysosulfatide (sulfogalactosyl‐sphingosine). Sphingosine strongly stimulates (Ka= 0.16 μM) the PPase activity, assayed both as ΔpH formation across the tonoplast vesicle membrane, and as reversible clamp current measured by the whole‐vacuolar mode of the patch‐clamp technique. Psychosine showed a minor, and lysosulfatide no stimulatory effect. No effect upon the ATPase activity has been observed. No sphingosine‐induced change could be observed in the affinity of the PPase for its substrate (apparent Km= 10 μM MgPPi). We tentatively conclude that sphingosine, which is known as a potent inhibitor of the protein kinase C in animal cells, may be a regulator of the plant vacuolar PPase.