Enzyme levels in chick embryo heart and brain from 1 to 21 days of development☆

[摘要] Enzymeactivitylevelsweremeasuredinchickembryobrainandheartduringdevelopment,beginningwithmedullaryplateandcardiogenicmesentoderm.Tostudyheartandbrainduringtheperiodofmorphogenesis(1–4days)amethodforfreezedryingwholechickembryoswasdeveloped.Inthreedivisionsofbrain—diencephalon,telencephalon,andhindbrain-hexokinase,glyceraldehyde-3-Pdehydrogenase,and6-P-gluconicdehydrogenasemaintainedapproximatelyconstantlevelsofactivityduringthisperiod.Brainglucose-6-Pdehydrogenaselevelsfellsomewhat,butcontrarytoearlierreportsshowednowidefluctuations.Inheart,glucose-6-Pdehydrogenaseactivityfelltoone-halfbetween1and4days,6-P-gluconicdehydrogenaseactivityremainedconstant,whilehexokinaseactivitydoubledinatriumfrom1to2days,andtripledinventriclefrom1to4days.From6to21daysofdevelopment,homogenatesofheartsandbrainswereused.Hexokinaseactivityinbrainincreasedfour-foldduringthisperiod,whileinheartthespecificactivitydidnotchange.Glyceraldehyde-3-Pdehydrogenaseactivityshowednochangeineitherorgan.NAD-dependentisocitricdehydrogenaseincreasedinbothheartandbrain,fourfoldinbrain,nearlytwofoldinheart.α-Ketoglutaricdehydrogenaseincreased50%inbrainand250%inheart.Theincreasinglevelsofcitricacidcycleenzymesprobablyreflectanincreasingenergydemandinbothorgansduringthelast2weeksbeforehatching.Sinceadultbraindependsprimarilyuponglucoseforenergy,itseemsreasonablethatthehexokinaseactivitycontinuedtoincrease.Adultheart,however,obtainsitsenergyfromsubstratesotherthanglucose,whichmayaccountforthefactthatduringthelast2weeksnochangeinhearthexokinaseactivitywasseen.

[学科分类] 生物科学（综合）