Rhodopsin

Introduction

All-trans-retinalcanfurthercausetheconformationalchangeoftheopsinmolecule,andbegintoseparatefromtheopsinpart,andthencontinuetoseparateundertheactionoftheenzymeuntilitisdecomposedintotwoMolecule,thedecomposedall-trans-retinalcannotdirectlycombinewithopsintoformrhodopsin,butitcanbereducedtovitaminAundertheactionofvitaminAenzyme.Itisusuallyall-transandstoredinpigmentepithelialcells.,Andthenentertherodcells,andthenoxidizedinto11-cisretinal,participatinginthesynthesis,supplementationanddecompositionofrhodopsintocontinue.

Synthesis

Thefirststepinthesynthesisofrhodopsinistoturnall-trans-retinalinto11-cis-retinal.Thisstepisinthedark,undertheactionofenzymes.Whatisdonenextisanenergy-consumingreaction,andtheequilibriumpointofthereactionisdeterminedbytheintensityoflight.Thesecondstepistosynthesizerhodopsinwithopsinonce11-cis-retinalisproduced.Thisstepdoesnotconsumeenergyandcanbecompletedquickly.AlthoughtheconversionbetweenvitaminAandretinalisreversible,becausepartoftheretinalhasbeenconsumedduringthereaction,itmustrelyonthesupplyofvitaminAintheblood.HumansandhigheranimalscannotsynthesizevitaminAbythemselves,butmustbeingestedfromfood.PatientswithvitaminAdeficiencycannotseeobjectsclearlyinthedarkatnight.ThiskindofnightblindnesscanbecuredbysupplementingfoodsrichinvitaminA.

Conecellresearch

Inrecentyears,accordingtothemeasurementoftheabsorptionspectraofsingleconecellsinprimatesandhumanfreeretinas,ithasbeenfoundthattherearethreetypesofconecellswithpeakabsorptionspectra.Theyare450nanometers(blue),525nanometers(green)and550nanometers(red).Thisshowsthatthereareprobablythreedifferentconephotosensitivepigments.Thepurificationandseparationofthephotosensitivepigmentsofthethreetypesofconecellshasnotbeensuccessful.However,atpresent,aphotosensitivepigmenthasbeenextracted,thatis,therhodopsin(iodopsin)extractedfromtheretinaofchickenscontainingonlyconecells.Itsspectralabsorptionpeakpositionisequivalenttotheredlightregion.ItisalsoretinalandThecombinationofopsinandrhodopsinisonlyslightlydifferentinopsin.Thelightsensitivityofphotoreceptorcellsiscloselyrelatedtotheamountofphotoreceptorpigmentsthathavenotbeendecomposed.Averysmalldecreaseintheconcentrationofphotosensitivepigmentswillgreatlyreducethephotosensitivityofphotoreceptorcells;whentherhodopsininthehumanretinaisdecomposedby0.50%,thephotosensitivityofrodcellswilldropbyasmuchas2000times.Therefore,duringdarkadaptation,thelevelofretinallightsensitivityiscloselyrelatedtotheratioofsynthesisanddecompositionofrhodopsin,especiallytherecoveryofrhodopsin.After20-30minutesofdarkadaptation,thevisualsensitivityreachesthehighestvalue,andtherhodopsinisalmostcompletelyrestored.