Metabolism of inositol 1,4,5-trisphosphate in squid photoreceptors |
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Authors: | Susan F. Wood Ete Z. Szuts Alan Fein |
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Affiliation: | (1) The Marine Biological Laboratory, 02543 Woods Hole, MA;(2) Boston University Marine Program, 02543 Woods Hole, MA;(3) Department of Physiology, Boston University School of Medicine, 02118 Boston, MA, USA;(4) Department of Physiology, University of Connecticut Health Center, 06032 Farmington, CT, USA;(5) Present address: Dept. of Neuroscience, The Johns Hopkins University School of Medicine, 725 N. Wolfe St., 21205 Baltimore, MD, USA |
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Abstract: | Summary Inositol 1,4,5-trisphosphate (InsP3) is rapidly formed in squid photoreceptors in response to light, where it is converted sequenctially into inositol bisphosphate (InsP2) and inositol monophosphate (InsP1). All of the InsP3 appears to be degraded to inositol 1,4-bisphosphate via an InsP3-phosphatase, which is characterized in this study. The enzyme is water-soluble and present in the light-transducing distal segments of squid photoreceptors. It has a Km of 50 M for InsP3, requires Mg++ for its activity, is maximally active at neutral pH, specifically hydrolyses the 5-phosphate and is inhibited by 2,3-diphosphoglycerate. In these respects, InsP3-phosphatase of squid is very similar to the enzymes of other cells. Since no InsP4 or more highly phosphorylated inositols are found in squid photoreceptors, the InsP3-phosphatase may be important in the regulation of InsP3 concentration within these cells.Abbreviations InsP1, InsP2, InsP3, InsP4, InsP6 inositol monobis-, tris-, tetrakis-, hexakisphosphate, respectively - 2,3-DPG 2,3-diphosphoglycerate - EDTA ethylene diamine tetraacetic acid - DTT dithiothreitol - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - PMSF phenylmethylsulfonyl fluoride |
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Keywords: | InsP3-phosphatase Photoreceptors Squid Inositol phosphates Inositol trisphosphate |
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