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

Abstract

The interaction of rabbit muscle myosin (M), heavy meromyosin (HMM) and light meromyosin (LMM) with the amphiphiles sodium linoleate (L) and sodium n-dodecyl-sulphate (SDS) in aqueous solutions has been investigated by microcalorimetry. At pH 6.4, M and LMM interact endothermically with L whereas for HMM at pH 6.4, and M, HMM and LMM at pH 8.0, the interaction is exothermic. A significant exothermic thermal transition is found at pH 6.4 for the interaction of M with L at a ratio of approximately 0.1 mmol L per mg M which can be associated with the HMM subfragment. The interaction enthalpy for the linoleate-myosin and SDS-myosin systems are not additively related to those for linoleate and SDS interaction with the isolated subfragments, indicating that within the myosin molecule the subfragments do not interact with these amphiphiles independently, particularly at high amphiphile to protein ratios.