Light regulation of protein phosphorylation in Blepharisma japonicum

We demonstrate alterations in protein phosphorylation levels in light-expos ed Blepharisma using immunological and densitometric methods. The examinati ons show that cell illumination elicited a two-fold enhancement of phosphor ylation of a 46 kDa protein and a marked decrease in the phosphorylation of a 28 kDa protein over that measured in dark-adapted cells. The observed li ght-dependent changes in the phosphorylation levels of both proteins were e ntirely reversible. In contrast, no alteration in protein phosphorylation w as detected in cells treated by external potassium, which depolarizes the c ell membrane. These observations suggest that both the 28 kDa and 46 kDa pr oteins might be involved in the light transducing mechanism, which results in the photophobic response of Blepharisma.