Characterization of guanylate cyclase in squid photoreceptors

Vis Neurosci. 1989 Jul;3(1):1-7. doi: 10.1017/s0952523800012451.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cell Membrane / enzymology
  • Decapodiformes
  • Detergents / pharmacology
  • Enzyme Activation / drug effects
  • GTP-Binding Proteins / metabolism
  • Guanylate Cyclase / metabolism*
  • Light
  • Magnesium / pharmacology
  • Manganese / pharmacology
  • Photoreceptor Cells / enzymology*
  • Rhodopsin / metabolism


  • Detergents
  • Manganese
  • Rhodopsin
  • GTP-Binding Proteins
  • Guanylate Cyclase
  • Magnesium