Tropomyosin: a New Asymmetric Protein Component of Muscle

Abstract

AN unusual protein of fibrous character has been isolated from the fibrillar fraction of skeletal and cardiac muscle. It is simply prepared by washing away the sarcoplasmic components of finely minced muscle and dehydrating the residue in ethanol and then in ether. The debris, consisting mainly of stroma protein and of myosin denatured in situ, is soaked in a molar solution of potassium chloride at pH 7, when a clear viscous extract is obtained containing tropomyosin and other proteins which are then precipitated at pH 4.5. After redispersal at pH 7, the contaminating proteins are largely denatured, and are almost quantitatively removed in ammonium sulphate solutions of 41 per cent saturation. The tropomyosin, precipitated between 49 and 60 per cent saturation, is filtered, dissolved, dialysed and purified by repeating the isoelectric precipitation and salting-out procedures.