Proteolytic Activation of a Galactosyl Transferase Involved in Osmotic Regulation

Abstract
Osmotic regulation in the flagellate Ochromonas malhamensis Pringsheim is mainly mediated by changes in the pool size of .alpha.-galactosyl-(1 .fwdarw. 1)-glycerol (isofloridoside). Isofloridoside phosphate synthase, a regulated key enzyme responsible for the formation of isofloridoside phosphate, appears to exist as an inactive proenzyme which can be activated by incubation of crude cell extracts with endogenous or exogenous proteases.