Role of alpha-galactosidase in osmotic regulation of Poterioochromonas malhamensis

In Poterioochromonas malhamensis, osmotic regulation is mainly mediated by the formation and degradation of isofloridoside (α-galactosyl-1 → 1-glycerol). In cell homogenates an α-galactosidase can be demonstrated. About one hour after an increase in external osmotic pressure, the enzyme activity increases. The increase is more pronounced with a higher osmotic change and appears to be due to de novo synthesis of the enzyme, as it can be prevented by preincubation with actinomycin D or actidion. When the increase in α-galactosidase was suppressed with actinomycin D, the in vivo degradation rate of isofloridoside was slowed down. These results indicate a function of the α-galactosidase in osmotic regulation.