SOLUBILITY AND EXTRACTABILITY OF THE STRUCTURAL PROTEINS

In chapter 8 we were concerned with the growth of knowledge of actomyosin- ATP interactions from 1939 to about 1953. In chapter 9 we considered the theories of contraction (with their interesting variations) which resulted from the realisation of the importance of the actomyosin-ATP relationship. Here again the period chosen terminated about 1953, because at this time the idea of the sliding-filament mechanism began to emerge; as evidence has accumulated, this has gradually replaced almost all other postulated mechanisms. The story of this will occupy chapter 11. In the present chapter I want to discuss the properties of the individual structural proteins, to which another was added in 1946 by the discovery of tropomyosin by Bailey (2).

We have already discussed the results of earlier workers who estimated ‘myosin’, myogen, globulin X and stroma protein in muscle. After the discovery of actin and actomyosin, Balenović & Straub (1) were the first to try to estimate, albeit in an indirect way, the amount of actin present.

As the basis of this method they used the formation of actomyosin when actin was added to excess of myosin, the actomyosin being assessed by the fall in viscosity on addition of ATP. This decrease in specific viscosity as a function of the specific viscosity in presence of ATP, Straub (1) termed the ‘activity’ of unknown ‘myosin’ solutions, and he took the activity of myosin B solutions prepared from muscle in a standard way as 100%.