EARLY CHANGES IN BINDING BETWEEN DNA AND HISTONE IN HUMAN LEUCOCYTES EXPOSED TO PHYTOHEMAGGLUTININ

Previously reported changes in the deoxyribonucleoprotein (DNP) complex of human leucocytes responding to phytohemagglutinin (PHA) were further investigated in the present work by using the alkaline bromphenol blue (BPB) binding reaction for basic proteins. The extraction of DNA preceding the BPB-binding was performed both in trichloroacetic acid (TCA) and in picric acid (PA). TCA liberates both arginine and lysine residues for the subsequent BPB-binding. PA, which was found to bind strongly to the guanidino-groups of arginine, mainly liberates the lysine residues for the following BPB-binding. By measuring the amounts of PA and BPB bound after PA-hydrolysis and BPB staining, information was obtained about the relative amounts of arginine and lysine in histone bound to DNA. In PHA-treated cells a 25% decrease in BPB-binding was observed after TCA-hydrolysis. No such decrease in BPB-binding could be demonstrated after PA-hydrolysis. However, as much as an 80% decrease was found in the PA-binding capacity. These results were interpreted as a reduced number of arginine residues in histone bound to the DNA-phosphate groups in cells exposed to PHA. © 1969.