Conformational state of thin myofilament proteins in normal and chronically failing heart

Circular dichroism (CD) spectra of myocardial G-actin significantly differ from those of F-actin, and the spectra of G- and F-actins differ from those of myocardial tropomyosin, native tropomyosin and alpha-actinin. In heart failure in man and experimental animals, characterized by a significantly decreased ability of the contractile protein system to generate force, considerable changes in the tertiary structure of Straub G-actin are observed. During polymerization a monomer of this actin is included in F-actin as a promoter without corresponding conformational changes of a part of G-actin globule; G-actin from the failing myocardium loses its conformational mobility. According to CD data the secondary protein structure is not altered. CD spectra analysis with regard to the regions of aromatic amino acid residue localization in active sites of actin suggests that the sites of actin-myosin and actin-actin interactions do not assume the conformation necessary for normal functioning of thin filaments.