ACTIVATION OF BOVINE PHOTORECEPTOR GUANYLATE-CYCLASE BY S100 PROTEINS

S100 proteins are acidic calcium-binding proteins present in high conc entration in the brain and at lower concentrations in peripheral tissu es. Their function remains to be elucidated in many tissues. In this r eport we show for the first time that S100 proteins stimulate the bovi ne photoreceptor membrane guanylate cyclase. The extent of stimulation varied between the different S100 proteins with the S100b exhibiting the highest level of influence. The stimulation by all S100 proteins w as calcium dependent, with the half-maximal stimulation occurring at a bout 35-40 mu M calcium. These results suggest that in some cells S100 proteins can mediate calcium signals via cyclic GMP. (C) 1996 Academi c Press, Inc.