Synthesis of experimentally induced glutamine synthetase (glutamotransferase activity) in embryonic chick retina in vitro☆

[摘要] Thephenomenonofprecociousappearanceandrapidenhancementofglutamotransferaseactivityofembryonicchickneuralretinainresponsetoexplanationinvitrohasbeensubjectedtomoredetailedscrutiny.Onthebasisofcofactorrequirements,pHoptima,responsetospecificinhibitors,andratiooftransferasetosynthetaseactivity,theenzymeundergoingchangewasclassifiedasaglutaminesynthetase.Testsforthepresenceofenzymeactivatorsand/orinhibitorsundergoingchangeduringincreaseinenzymeactivitywerenegative,suggestingthatincreaseinactivitywasduetosynthesisofnewenzyme.Thiswassubstantiatedbythefindingthatlowlevelsofpuromycinblockedcompletelyandreversiblyincreasesinenzymeactivityundercultureconditions;andthatactinomycinDsimilarlyblockedsuchincreasesirreversibly.Preexistinglevelsofactivityappearedstableinthepresenceofeitherinhibitor.Thesedatawereinterpretedtomeanthatenhancementofglutamotransferaseactivitywhichoccursincultureisduetosynthesisofnewenzyme;italsosuggestedalabilityoftheRNAinvolvedandconsequentlyaratherdirectgenomiccontrolovertherateofsynthesisoftheenzymeinearlyontogenesis.Pigmentedepitheliumofembryoniceye,vitreoushumor,andembryoextractshowednoeffectontheincreaseinglutaminesynthetaseactivityintheexplantedretina;thiswasinterpretedasdiminishingbutnotexcludingthepossibilitythatastable,diffusiblesystemicfactorisresponsibleforcontrolofearlyontogenesisofthisenzymeintheembryo.Glutamine,glutamate,andγ-aminobutyratewerefoundtolowersynthesisoftheenzymeinculturewhenaddedtothemedium,butnoneoftheseaminoacidsappearedcapableoftotalrepressionatconcentrationsapproachingphysiologicalvalues.Glutathione(oxidizedandreduced),asparagine,aspartate,andglucoseallhadnodemonstrableaffectuponthegrowthoftheenzymeinculture.

[学科分类] 生物科学（综合）