Influence of carbamoylation on some analytical properties of basic polypeptides

The effect of carbamoylation on the assay or identification of histones and polylysine was investigated. Incubation with sodium cyanate decreased the positive charge on these polypeptides as judged by changes in the binding of methyl orange or the electrophoretic mobility. Histones in chromatin appeared less accessible to carbamoylation than isolated histones. Carbamoylation of proteins under conditions in which there was little or no effect on the Lowry procedure could affect their assay by methods utilizing metachromasia with Coomassie Blue G. The Bradford assay has low sensitivity for HI histone and polylysine but this can be increased by preincubation with sodium cyanate. More extensive carbamoylation of polylysine caused decreased sensitivity which was the only response seen with core nucleosomal histones and bovine serum albumin when preincubated with sodium cyanate. It was concluded that the sensitivity for HI histone and polylysine in assays dependent on metachromasia with Coomassie Blue G may be changed by factors which decrease the positive charge on these polypeptides.