Experimental studies on a mutant gene, a, causing albinism in the axolotl, Ambystoma mexicanum☆

[摘要] Axolotlswhicharehomozygousforthegene,a,aretruealbinos,i.e.,theylackcompletelytheabilitytosynthesizemelanin.Previousinvestigations(C.P.Benjamin,1970;Develop.Biol.23,62–85)showedthathomogenatesofalbinoembryosorlarvae,unlikethoseofnormallypigmentedaxolotls,areunabletocarryoutmelaninsynthesiswhensuppliedwithl-dopa.Thisresultshowedthattyrosine-dopaoxidase(TDO),theonlyknownenzymeinthemelaninpathway,isinactiveinalbinos.Thepresentinvestigationhasshownthat,thoughthealbinolacksTDOactivity,theenzymeitselfispresentandcanbeactivatedbyproteolyticenzymes.ImmuneprecipitationofTDOfromfreshcrudeskinextractsandcomparisonoftheprecipitatesonSDS-polyacrylamidegelsrevealsthattheinactivesubunitsfromalbinosamplesaresome8000daltonslargerthantheactivesubunitsfromwild-typesamples.Activationapparentlyconsistsofthecleavageofacovalentlyboundfragment(s)fromtheproenzyme.AlbinoskinhomogenatesalsocontainaTDOinhibitoryfactorspecificforaxolotlTDO.Evidenceispresentedthatsuggeststhattheinhibitorinteractsreversiblywiththeproenzymeandirreversiblywiththeactiveform.Amodelispresentedthatproposesthat,inwild-typeaxolotls,theAgeneisresponsibleforthenormalactivityofaTDOactivator.Inthealbinotheactivatordoesnotfunctionproperlyandthisresultsinthecontinuedpresenceoftheinhibitorandofthelatentformoftheenzyme.

[学科分类] 生物科学（综合）