Alkaline Denaturation of Nucleohistone.

The ultraviolet spectral change at 245 nm of tyrosine residues in histones in alkaline solution was studied. The difference spectrum of histones between alkaline and neutral solution yields an absorption maximum at 242 nm. However, the influence of configurational changes of backbone structure of histones in alkaline solution, results in the true peak position being located near 245 nm. This was established from artificial difference spectra between histones and N-acetyl-L-tyrosine ethyl ester in 0.5 N NaOH, conditions under which ionization of phenolic hydrogens of histones is immediately complete. This ease of ionization permits the quantitative estimation of histones in nucleohistone by measuring the ratio of absorbance at 244 nm to that at 260 nm. so long as we can prepare the nucleohistone from calf thymus which does not contain nonhistone protein. Alkaline spectrophotometric titration of nucleohistone revealed that conformational changes of histones occur when the double helical structure of DNA is in the process of disruption in a nucleohistone molecule. This conformational change occurred without the dissociation of histones and DNA. The dissociation of histones and DNA in alkaline pH region was discussed. [ABSTRACT FROM AUTHOR]