The decrement in light sensitivity of the isolated frog retinal rod in the presence of a phosphorylation-resistant GDP analogue of guanosine-5′-O-(2-thiodiphosphate) as a confirmation of the hypothesis about transducin activation via the transphosphorylation mechanism

The decrement in light sensitivity of the isolated frog retinal rod cell was demonstrated after a short-time perfusion with guanosine-5′-O-(2-thiodiphosphate), which is an analog of GDP that is resistant to phosphorylation by nucleoside diphosphate kinase. This decrement can be explained by the hypothesis that transducin, which is the main GTP-binding protein of the retinal rod photoreceptor of vertebrates, is activated by phosphorylation of bound GDP to GTP; this is induced by the activated rhodopsin receptor. The results can be considered as a confirmation of the proposed hypothesis.