title: Characterization of guanylate cyclase in squid photoreceptors.
abstract: Light causes a rapid, 1.7-fold increase in cyclic GMP concentration in intact squid retinas (Johnson et al. (1986]. To determine whether light-induced changes in cyclic GMP concentration result from activation of guanylate cyclase, we have studied the regulation of guanylate cyclase activity in squid (Loligo pealei) photoreceptors. The enzyme is membrane-associated and activity is enhanced by the detergents Triton X-100 or digitonin. The enzyme requires divalent cations, Mn2+ being preferred over Mg2+. The dependence of enzyme activity on the MnGTP concentration deviates from simple Michaelis-Menten kinetics. Under conditions where a light-induced binding of GTP to the guanine nucleotide regulatory protein can be observed, no light-induced change in guanylate cyclase could be detected.
authors.affiliation: Department of Biology, Brandeis University, Waltham, MA 02254.
authors.forename: P R
authors.initials: PR
authors.lastname: Robinson
authors.forename: R H
authors.initials: RH
authors.lastname: Cote
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D049832:Decapodiformes; D003902:Detergents / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism; D006162:Guanylate Cyclase / Q000378:metabolism*; D008027:Light; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D010786:Photoreceptor Cells / Q000201:enzymology*; D012243:Rhodopsin / Q000378:metabolism
chemical_list: D003902:Detergents; D008345:Manganese; D012243:Rhodopsin; D019204:GTP-Binding Proteins; D006162:Guanylate Cyclase; D008274:Magnesium