Utilization of cystine-S35 by the chick embryo

Abstract

Fertile eggs from controlled flocks were injected with 10 µc l-cystine-S35 (specific activity 5.71 µc/µmole) and incubated under standard conditions of humidity, circulation, and temperature. Beginning with the 5th day, embryos were hydrolyzed (6 N HCl, 6 hr, 15 lb) and chromatographed using ascending strip chromatography. Cystine and methionine were determined colorimetrically following elution; radioactive assay was done on the eluates; and the specific activity of both cystine and methionine was determined. The specific activity of cystine at 5 days was .0092 and increased generally until the 20th day (.0692). The specific activity of methionine at 9 days was .0104, at 16 days was .0490, and at 20 days was .0132. The per cent of the dose recovered as cystine at 20 days was 22.21 and that recovered as methionine was 2.03. The data for specific activity indicate that the fractional composition of embryonic protein relative to cystine and methionine is not constant and that there is considerable sulfur transfer between cystine and methionine.