title: Characterization of a calcium/calmodulin-dependent protein phosphatase in the Limulus nervous tissue and its light regulation in the lateral eye.
abstract: Calcium (Ca2+) plays an integral role in the light response of the photoreceptors in both vertebrate and invertebrate organisms. In the ventral eye of the horseshoe crab, Limulus polyphemus, a flash of light delivered to a dark-adapted photoreceptor stimulates a rapid rise in intracellular free calcium concentration ([Ca2+]i), which in turn mediates light adaptation. It has previously been demonstrated that in Limulus photoreceptors light, via Ca2+, activates a calcium/calmodulin (Ca2+/CaM)-dependent protein kinase which increases the phosphorylation of arrestin. We now have identified biochemically, a calcium/calmodulin-dependent protein phosphatase (Ca2+/CaM PP) in homogenates of the Limulus lateral and ventral eye, brain, and lateral optic nerve using as a substrate, a 32P-labeled peptide fragment of the regulatory subunit of cAMP-dependent protein kinase (RII). This protein phosphatase shares biochemical properties with calcineurin, a Ca2+/CaM-dependent protein phosphatase (type-2B). Its activity is enhanced by Ca2+, calmodulin and Mn2+; and is inhibited by mastoparan, a calmodulin antagonist, and a synthetic peptide corresponding to the autoinhibitory domain of mammalian calcineurin. Most importantly, light regulates the Ca2+/CaM PP activity in the lateral eye. While there is no difference in basal activity in long-term dark- or light-adapted preparations, Ca2+ enhances Ca2+/CaM PP activity only in long-term light-adapted eyes.
authors.affiliation: Department of Biology, University of South Florida, Tampa 33620.
authors.forename: D Z
authors.initials: DZ
authors.lastname: Ellis
authors.forename: S C
authors.initials: SC
authors.lastname: Edwards
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology*; D019703:Calcineurin; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002148:Calmodulin-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003623:Dark Adaptation; D006737:Horseshoe Crabs; D036341:Intercellular Signaling Peptides and Proteins; D008027:Light; D008969:Molecular Sequence Data; D009900:Optic Nerve / Q000187:drug effects / Q000201:enzymology; D010446:Peptide Fragments; D010455:Peptides; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000187:drug effects / Q000201:enzymology*; D015398:Signal Transduction / Q000502:physiology; D013379:Substrate Specificity; D014862:Wasp Venoms / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D010455:Peptides; D014862:Wasp Venoms; C037500:mastoparan; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D002118:Calcium