Effect of formaldehyde on the circular dichroism of chicken erythrocyte chromatin.

Formaldehyde (HCHO) fixation of chicken erythrocyte chromatin produces a marked decrease in its positive circular dichroism (CD), above 260 nm, and the appearance of s small negative ellipticity around 295 nm. The ultraviolet spectrum of chromatin is unaffected, nor does HCHO produce any changes in the uv or CD spectra of chicken erythrocyte DNA. The extent of the circular dichroism transition from the native chromatin to the suppressed spectrum is dependent on the concentration of HCHO and salt concentration. The kinetics of the reactions are complex, implicating at least two reactive species. Studies of the reaction of HCHO with chromatin in ethylene glycol and CD measurements of aqueous chromatin solution with added glutaraldehyde preclude simple dehydration and general cross-linking effects as causes of the CD changes observed. The results are interpreted as indicating a conformational change of the DNA in chromatin caused by histone-DNA or histone-histone cross-linking.