Studies of muscle development. VI. Identification of tropomyosin and troponin and quantitation of tropomyosin in embryonic and mature chick leg muscle

Tropomyosin was quantitated in embryonic and postembryonic chick leg muscle by a procedure involving acrylamide gel electrophoresis, with subsequent elution of tropomyosin from the gels, followed by adsorption on membrane filters and subsequent extraction and spectrophotometric determination of a dye-tropomyosin complex. Tropomyosin was present at low levels of 20 mg/100 g muscle at 11 days of incubation and increased to 360 mg/100 g muscle at 2 months of development. The accumulation data for tropomyosin parallel those of myosin throughout development. Chicken tropomyosin in the presence of unfractionated chicken troponin (troponin A and B) confers EGTA sensitivity to Mg²⁺-activated desensitized actomyosin. The presence of troponin B activity in the unfractionated preparation is evident since the troponin preparation in the absence of tropomyosin inhibits superprecipitation of Mg²⁺-activated desensitized actomyosin. In this respect chick tropomyosin and troponin are similar to the corresponding rabbit protein.