Quantitative Changes in Contractile Proteins of Chick Skeletal Muscle During and After Embryonic Development

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Abstract
Detns. of the contractile proteins actomyosin and myosin were carried out with viscosimetric methods in muscle tissue of developing chick embryos. Actomyosin was found to be less than 1 mg./g. of tissue wet weight before the 12th day of incubation. The concn. of actomyosin in muscle tissue increases rapidly after this day and reaches the adult level of about 50 mg./g. of tissue on the 50th day of development. Small quantities of myosin are probably present before the 12th day of development. Since fibrillation and cross-stria-tion have been observed in chick muscle between the 7th and 9th day of development the formation of quantitatively significant amts. of contractile proteins seems to occur at a relatively late stage of development.