Native and denatured muscle proteins

Abstract

Meyer and Weber (1933) have recently proposed the addition of a third protein to the accepted constituents of muscle plasma, von Fürth’s myosin and myogen. The evidence for the existence of “Globulin X ”, as it is tentatively named, is based on the examination of the precipitates formed during the dialysis of muscle press-juice and salt extracts. The salt-soluble fraction of the precipitate from muscle juice differs little from myosin in its isoelectric point, but it differs widely in its solubility in salt solutions and in the low viscosity of such solutions and their freedom from stream anisotropy. The clean separation of the muscle protein fractions is rendered difficult by the readiness with which certain of them undergo denaturation. Not only does the formation of denaturation products multiply the number of individual substances present in press-juice and extracts, but the products themselves, although insoluble, form refractory suspensions which interfere with centrifugation and filtration. The object of the present work has been twofold: firstly, to ensure that denaturation products or complexes formed between native and denatured protein have not been mistaken for new native proteins; and secondly, to investigate the possibility of preparing cleanly separated fractions for the purpose of chemical and physico-chemical studies. The assurance of a pure preparation is particularly desirable in the case of myosin, which is at the present time receiving much attention in view of its importance in the physiology of muscular contraction.