EFFECT OF TEMPERATURE AND pH ON PROTEIN‐PROTEIN INTERACTION IN ACTOMYOSIN SOLUTIONS

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Abstract
The extent of protein‐protein interactions in actomyosin solutions was measured as a change in light scattering absorbance of a solution undergoing change. The extent of the reaction registered as an increase in light scattering absorbance indicating an increase in the size of the macromolecules. In treatments where the extent of protein‐protein interaction was extensive, film formation and/or precipitation of the macromolecules occurred. At constant protein concentration the kinetics of the reaction was dependent upon temperature, pH and the type of actomyosin used. In general, the rate and maximum extent of change increased with increasing temperatures and decreasing pH. Below 40° C more change was generally observed in beef actomyosin solution compared to mackerel at the same temperature and pH. However, at higher temperatures, mackerel actomyosin often shows more change than beef under the same conditions. The shapes of the reaction curves were such that the slope of the steepest line that can be drawn from the origin to tangent the curve at the region where the change starts to taper off (the characteristic slope), was a good index of the rate of change and the maximum extent of interaction attained. Arrhenius‐type plots of the characteristic slopes showed three possible mechanisms of change predominating within certain temperature ranges, as indicated by well‐defined inflections in the curves, reflecting varying activation energies for the reactions. The three temperature zones are: below 40°C; between 40 and 60° C; and above 60° C. Below 40° C the rate and maximum extent of protein‐protein interaction is very strongly temperature dependent.

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