Extraction of proteins other than myosin from the isolated rabbit myofibril

Abstract

On exhaustive extraction of rabbit myofibrils with buffers of low ionic strength, pH 7.1-8.3, 25-36% of the total myofibrillar protein passed into solution. This extract contained tropomyosin, an inactive form of actin and an unidentified protein provisionally named component C. Tropomyosin accounted for at least 10-12% of the total myofibrillar protein. The inactive form of actin extracted from myofibrils was electrophoretically identified with F actin inactivated by dialysis against 0.78 [image] borate buffer, pH 7.1, but not with F actin inactivated by treatment with K I. When the extract obtained by treating myofibril with solutions which are considered to remove the A band selectively was dialyzed against 0.04 [image]KC1 containing 6.7 m[image] phosphate, pH 7.2, 3-7% of the total myofibrillar N remained in solution.