Volume Regulation in Poterioochromonas

Publisher Website
Google Scholar
Abstract
In Poterioochromonas malhamensis Peterfi (syn. Ochromonas malhamensis Pringsheim) osmotically induced shrinkage is reversed by an accumulation of isofloridoside. Addition of Ca2+ ions to homogenates from standard volume cells initiates an enzyme system for the activation of isofloridoside-phosphate synthase. This process is stimulated in the presence of Ca2+ by calmodulin, isolated from the same alga or from bovine brain, and requires the presence of membranes. The stimulation observed when Ca2+ is added without exogenous calmodulin is inhibited by the calmodulin-binding substance R 24571. These results show that the effect of Ca2+ is mediated by calmodulin. The Ca2+/calmodulin-dependent activation is enhanced when fluoride or molybdate ions are present in the homogenization buffer. This might indicate the involvement of a phosphorylated compound in the activation mechanism.