A 26 kd calcium binding protein from bovine rod outer segments as modulator of photoreceptor guanylate cyclase

摘要: The resynthesis of cGMP in vertebrate photoreceptors by guanylate cyclase is one the key events leading to reopening cGMP-gated channels after photoexcitation. Guanylate activity rod outer segments dependent on free calcium concentration. basal enzyme observed at high concentrations (greater than 0.5 microM) increases when concentration lowered into nanomolar range (less 0.1 microM). This effect known be mediated a soluble calcium-sensitive protein highly cooperative way. We here show that this protein, i.e. modulator photoreceptor cyclase, 26 kd protein. Reconstitution purified with washed segment membranes containing revealed 3- 4-fold increase was physiological from microM 4 nM. whole stimulated 10-fold same range. activation process reconstituted system similar native preparation, it showed cooperativity Hill coefficient n between 1.4 and 3.5. half-maximal occurred 110 220 nM calcium. molar ratio rhodopsin 1:76 +/- 32. binding as detected 45Ca autoradiography. Partial amino acid sequence analysis 60% homology visinin chicken cones.