Formaldehyde and glutaraldehyde in the fixation of chromatin for electron microscopy

Glutaraldehyde and formaldehyde have been used to fix chromatin core particles for electron microscopy. Glutaraldehyde crosslinks protein only, whereas formaldehyde crosslinks protein and DNA. This is confirmed by the observation that the detergents sodium dodecyl sulphate, Sarkosyl NL 35 and benzylalkyldimethyl ammonium chloride separate the DNA from the protein in the case of glutaraldehyde fixed core particles but not in the case of formaldehyde fixed core particles. The fixative used in the preparation must therefore be considered as a further variable when evaluating electron microscopic images of chromatin.