Formation of sulphydryl peptides of low molecular weight in HeLa cells after irradiation

PCMBS (p-chloromercuric-phenyl sulphonic acid), labeled with /sub 203/Hg was used to determine -SH containing peptides formed after irradiation of HeLa cells. Sulphydryl groups of peptides bind firly and specifically with PCMBS and the labeled compound bound to the -SH containing cell components was separated from unbound PCMBS on the basis of molecular size by Sephadex chromatography. Comparison of control and irradiated cell components showed very few qualitative differences, but significant quantitative differences were observed in the amino acid composition of the low-molecular-weight components separated on the G25 column. Very large increases in aspartic and glutamic acids, threonine, serine, and alanine were observed after irradiation. Studies of -SH components separated by G100 Sephadex showed that a redistribution of -SH had occurred after irradiation and that components formed were probably smaller than 5000 in m.w. The use of G25 columns demonstrated that most -SH components had a molecular weight within range of a few hundred, probably 100 to 400. G10 column fractionations confirmed the existence of small di- or tripeptides in addition to cysteine itself. (UK)