Inositol trisphosphatase and bisphosphatase activities in the retina of crab.

Inositol trisphosphate appears to be an excitatory second messenger in the transduction cascade of invertebrate visual photoreceptors. The high time-resolution of visual transduction demands an efficient system for the removal of the second messenger. It is now demonstrated that soluble extracts of crab retina promote rapid magnesium-dependent release of inorganic phosphate from D-myo-1,4,5,-inositol trisphosphate. Experiments in which the inositol trisphosphate had been labelled with 32P in the 4' and 5' positions indicated that both inositol trisphosphatase and bisphosphatase activities are present. The breakdown involves loss of at least one of the pair of vicinal phosphates, which is sufficient to inactivate the compound.