EFFECTS OF FIXATIVES ON HIGH-ORDER CHROMATIN STRUCTURE - A CALORIMETRIC STUDY

Differential scanning calorimetry has been carried out on native calf thymus cells in order to investigate, by a non-invasive tool, the effects of the most common fixatives at the level of higher order chromatin structure. Therefore the effects of 2% glutaraldehyde in saline buffer and ethanol acetic acid 3:1 v/v mixture have been analysed: the first one is known to induce cross-linking between the various cell constituents, and the second one induces dehydration. Looking at the thermal profiles the disappearance of all four transitions and the appearance of a new single broad transition at 390 K are the most remarkable effects following the glutaraldehyde fixation of thymocytes. In contrast ethanol/acetic acid causes a reduction of the protein melting at 345 K, a loss of the 375 K transition and a shift of the 360 K transition. These data are explained in terms of opposite dramatic chromatin structure changes.