The interaction of malonaldehyde with myosin and its subfragments: a microcalorimetric study

Abstract

The enthalpies of interaction between malonaldehyde and myosin (M) and its subfragments, heavy meromyosin (HMM) and light meromyosin (LMM) in aqueous solution (pH 6.8) at 25°C have been measured as a function of malonaldehyde concentration by microcalorimetry. The interaction enthalpies are all endothermic reaching saturation values of approximately 60 J g −1 (M) and 110 J g −1 (HMM). The enthalpies of interaction between malonaldehyde reactive amino acids have been measured under the same conditions and used to derive contributions of the reactive side chains of amino acid residues to the overall enthalpies of the myosins-malonaldehyde interactions. It is found that the enthalpies of reactions with the amino acid side chains in myosins cannot account for the large endothermic interaction enthalpies observed with malonaldehyde, but that the reactions initiate the denaturation of the myosins resulting in absorption of heat. Microcalorimetry is demonstrated to be a useful method of investigating the interaction of malonaldehyde with myosins on a relatively short time scale (20–30 min).