Conditioning of bovine muscle I.—Composition of the proteins of the myofibril

By selective extraction, precipitation and separation on diethylaminoethyl cellulose the proteins of the myofibril have been divided into a number of fractions which, quantitatively, do not vary in the longissimus dorsi muscles of six different beef animals. The fractions have been analysed by starch‐gel electrophoresis and some have been found to consist of almost pure proteins while others are complexes. About 80–85 % of the myofibrillar protein could be extracted of which 47% was myosin, 12% tropomyosin and 3% troponin. The amount of actin could not be determined since it appeared partly as complexes with α‐actinin, with troponin, and with the insoluble residue.