In Vitro Activation of a Galactosyl Transferase Involved in the Osmotic Regulation of Ochromonas

Abstract

Osmotic regulation in the flagellate O. malhamensis Pringsheim was mainly mediated by fluctuations in the pool size of .alpha.-galactosyl-(1 .fwdarw. 1)-glycerol (isofloridoside). A regulated key enzyme of isofloridoside metabolism was the galactosyl transferase producing isofloridoside phosphate. The activity of this enzyme in crude extracts can be increased 5-20-fold by incubation at pH 6. The activation occurs in a reaction with a Q10 of 1.5-3 and is dependent on time and pH value. Inactivation of the activated form of the enzyme is also time-dependent, and is minimal at the pH value at which activation is optimal. The data suggest a regulation of the enzyme by chemical modification due to the action of auxiliary enzymes.