The identification of randomly formed thin filaments in differentiating muscle cells of the chick embryo☆

[摘要] Theappearanceofthinfilaments,60–80Ã…inwidth,inthemyoblastsofearlychickembryosincubatedfor3daysat39°Cwasobservedwiththeelectronmicroscope.Thefilamentsweredistributedrandomlythroughoutthecytoplasmicmatrixofthemyoblastswheremyofibrilshadnotyetbeenformed.Thesefilamentswereisolatedfrom4-dayembryosbydifferentialcentrifugation;theywerefoundinthetoplayersoftheso-called“microsomalfraction.”ThefractionshowedconsiderableflowbirefringenceandanATPaseactivity.Mixingofthefractionwithrabbitmyosincausedmarkedincreaseintheflowbirefringence,andtheadditionofATPtothemixturein0.6MKClsolutionresultedinadecreaseinthebirefringence.TheATPaseactivityofmyosinwasenhancedabout100%bytheadditionofthefractionatlowionicstrength.NochangesinbirefringenceorATPaseactivitytookplacewhenactinwasaddedtothefraction.Thedemonstrationofthereactionofthe“microsomalfraction”withaddedmyosinstronglysuggeststhatthethinfilamentsinquestionareF-actinfilaments.

[学科分类] 生物科学（综合）