Myosin salt effects

In resting muscle the high concentration of ADP does not decrease the proton gradient effectively and the high membrane potential slows electron transport. ADP, formed when ATP is hydrolyzed by myosin ATPase during contraction, may stimulate electron transport. However, the concentration of ATP (largely as its Mg salt) is buffered by its readily reversible formation from creatine phosphate catalyzed in the intermembrane space, and in other cell compartments, by the various isoenzymes of creatine kinase (reviewed by Walliman et al., 1992). 

Onishi, H., Kojima, S., Katoh, K., Fujiwara, K., Martinez, H. M., and Morales, M. F. (1998). Functional transitions in myosin Formation of a critical salt-bridge and transmission of effect to the sensitive tryptophan. Proc. Natl. Acad. Sci. USA 95, 6653-6658. 

Among the above hypotheses, effects of lipids (4-17,59-62, 69-71,155-159), formaldehyde (160-166), and gas-solid interface TMJ appear to be very important in Gadoid fishes. Denaturation of myofibrillar proteins caused by free fatty acids and/or lipid peroxides must occur during frozen storage. To prove this, Jarenback and Liljemark have shown by electron microscopy that, in muscle stored frozen with added linoleic and linolenic hydroperoxides, myosin became resistant to extraction with salt solution (168). 

Myosin is another protein to which the theory of Linderstr0m-Lang in its present form is not applicable, since in myosin the ratio of molecular length to width is 100/1—far from the sphericity on which the theory is based. Thus experimental values of the parameter w cannot be easily interpreted quantitatively. Myosin is soluble in the presence of salt on the alkaline side of its isoionic point only, and thus should behave as a soluble protein above pH 5.7 to 5.8 and as an insoluble one below this. Mihdlyi (1950) has studied the effect of salt on the titration of myosin and reports that its insolubility in acid in the presence of greater than 0.05 M KCl does not affect the reversibility of the titration nor are there any obvious discontinuities in his titration curves, shown in Fig. 4. The data for basic solutions appear to be affected by salt very much as those of other soluble proteins, and reach an apparent limiting curve at a fairly low ionic strength (0.15). In acid solution where the protein is insoluble, however, the effect of salt closely resembles that for wool, except that the displacements of the parallel central portions of the curves are somew hat less than for wool, consistent with a lower affinity of myosin for chloride ion. The slopes of these portions of the curves are within 10 % of those observed for... 

All the known fibrous proteins of muscle are globulins which are insoluble at the isoelectric point (I.P.) in absence of salt (Table VI). This is true also of L-myosin which is sometimes described as water-soluble. In salt free solutions, Donnan effects are very marked as the pH is moved away from the I.P., and the protein swells and finally dissolves. 

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