The direct effect of protein starvation on protein breakdown and synthesis in regions of the cultured early chick embryo

Chick embryo explants of 11-13 somites (40 hours of preincubation) were exposed to¹⁴C-amino acids for 3 hours in liquid medium, cultured for 6 hours to reduce the trichloroacetic acid-soluble radioactive material, and then cultured on either protein starvation or growth media for periods up to 48 hours. The brain regions of explants cultured under starvation conditions lost larger quantities of radioactivity from protein than other regions of the embryo proper and the neural tube regions lost more radioactivity than the somites. The hearts of starved explants did not lose radioactivity. Explants cultured under growth conditions did not lose radioactivity from the regions of the embryo proper. Radioactivity was lost, however, from the protein of the extraembryonic membranes of explants cultured under both growth and starvation conditions. These basic observations were reproduced in experiments involving various¹⁴C-amino acids, the use of both growth and starvation conditions during the 6-hour preexperiment culture period, and the presence or absence of¹²C-amino acids in the final culture media. In an attempt to determine whether the regional differences in protein breakdown of starved explants were related to regional differences in protein synthesis, explants cultured for various periods on growth and starvation media were exposed to¹⁴C-amino acids for 90 and 180 minutes. The protein specific activities of embryo regions, corrected for regional differences in uptake and for the low overall specific activities of growing relative to starved explants, were comparable for growing and starved explants. This suggested that starvation did not differentially inhibit protein synthesis between regions of the embryo.