The mechanism of protein synthesis in the developing chick embryo. The incorporation of free amino acids

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Abstract
Free [C14]lysine is incorporated into protein by minced tissues of the 8-day chick embryo in vitro. The maximal incorporation rate is about 1.5 [mu]g. of lysine/mg. of protein/hr. The protein of all fractions of the cell was radioactive. At shorter time-intervals, the microsomes had the highest specific activity and percentage of the total activity. Dilution of the [C14]lysine with a large amount of [C12]lysine led to a rapid cessation of incorporation into the homogenate protein. The nuclear and mitochondrial protein also ceased to gain radioactivity. The radioactivity in the microsomal protein diminished, whereas the cell-sap protein continued to increase in specific activity at a high rate. Microsomes isolated from embryonic tissues at various ages incorporated free [C14]lysine and [C14]leucine into protein with cofactor requirements similar to those of microsomes from other sources. The results indicate that free amino acids are utilized by embryonic tissues by routes similar to those found in adult tissues, and at rates that could probably account for the requirements of the organism for protein synthesis.