The Influence of Ethylene Glycol on the Enzymatic Adenosine Triphosphatase Activity and Molecular Conformation of Fibrous Muscle Proteins.

Considerable interest has recently been evoked in the study of proteins in nonaqueous solvents, very largely as a result of the observations of Rees and Singer (1) and Yang and Doty (2) that the internal configuration of protein molecules could be radically altered in nonaqueous media, as reflected by changes in sedimentation constants, viscosity increments, and optical rotatory dispersion. Of the various organic solvents used in this connection, ethylene glycol is of particular interest since hydrophobic interactions in this solvent are weaker than in water solutions, and at the same time solute-solute hydrogen bonding occurs to about the same extent in both solvents. Significant studies dealing with the effect of ethylene glycol on globular proteins have been reported. Tanford et al. (3) were led to the conclusion that ethylene glycol is an unusually inert reagent towards globular proteins, in view of their observations that both y-globulin and @lactoglobulin, as revealed by optical rotation and sedimentation studies, retained their native conformations in water-ethylene glycol mixtures, up to a glycol concentration of about 75%. On the other hand, Sage and Singer (4) have presented potentiometric and spectrophotometric data which show that the conformation of ribonuclease in essentially anhydrous ethylene glycol is different from that in water solution. More recently, a study from our laboratory (5) has shown that among several organic solvents known to induce conformational changes in proteins, ethylene glycol most markedly influences the adenosine triphosphatase activity of cardiac myosin A; at levels of 45 volumes of ethylene glycol per 100 ml, the enzymatic activity is increased some 200% relative to a control myosin in 0.5 M KC1 alone. Further, this increase in enzymatic activity is accompanied by a marked decrease in the helical content of the molecule, as reflected by an increased bo (-147” in ethylene glycol as opposed to -374” in 0.5 M KC1 alone). This was considered as direct evidence that hydrophobic regions in the myosin molecule were implicated in the conformational change which gave rise to an increased enzymatic activity. In view of these findings with cardiac myosin, it was felt to be of interest to extend these parallel studies of enzymatic activity and conformation in ethylene glycol to other muscle proteins