X-ray microanalysis of protein sulphydryl groups in chromatin

A variety of evidence suggests that the protein sulphur in condensed chromatin tends to form disulphide bonds, whereas that in dispersed chromatin tends to exist as sulphydryl groups. X-ray microanalysis of mouse chromosomes showed a greater concentration of sulphur in heterochromatin than in euchromatin. Without the use of specific cytochemical reagents, it cannot be determined whether this sulphur in chromosomes is in the form of sulphydryls or disulphides. Two maleimides containing distinctive elements have been studied as X-ray cytochemical reagents for sulphydryl groups. Although adequate X-ray signals can be obtained from both, they give some non-specific staining, and do not appear to bind to all the available sulphydryl groups.