Molecular arrangement of troponin-T in the thin filament

1. Chymotrypsin cleaved troponin-T of skeletal muscle into two subfragments, i.e., troponin-T1 and -T2, each of which could be isolated by the use of DEAE-Sephadex. Troponin-T1 was a single subfragment with a molecular weight of 26,000 (chicken) or 22,000 (rabbit) daltons. Troponin-T2 consisted of two subfragments with molecular weights of about 13,000 daltons. Results obtained indicated that the smaller subfragment was formed by digestion of the larger subfragment of troponin-T2. 2. Antibodies against troponin-T1 and -T2 formed regular transverse striations along the whole length of thin filaments with 38 nm intervals, as was found reviously using antibodies against whole troponin complex as well as troponin components (Ohtsuki, I. et al., 1967; Ohtsuki, I. 1974 and 1975). 3. The first anti-troponin-T1 striation was situated 40 nm from the top of the filament. The first anti-troponin-T2 striation was 27 nm from the filament top and coincided with the first striations formed by antibodies against troponin-C or -I. 4. Troponin-T1 and the larger subfragment of troponin-T2 bound to tropomyosin which had been coupled to Sepharose, whereas the smaller subfragment of troponin-T2 did not.