Characterization of a calcium/calmodulin-depenAent protein phosphatase in the Limulus nervous tissue and its light regulation in the lateral eye

D. Z. Ellis, S. C. Edwards

Research output: Contribution to journalArticle

9 Scopus citations

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+]j), 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.

Original languageEnglish
Pages (from-to)851-860
Number of pages10
JournalVisual Neuroscience
Volume11
Issue number5
DOIs
StatePublished - 1 Jan 1994

Keywords

  • Calcineurin
  • Calcium
  • Calmodulin
  • Light regulation
  • Limulus polyphemus
  • Photoreceptor
  • Protein phosphatase

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