Localization of C-protein isoforms in chicken skeletal muscle: ultrastructural detection using monoclonal antibodies.

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Abstract
Monoclonal antibodies (McAb) specific for the fast (MF-1) and slow (ALD-66) isoforms of C-protein from chicken skeletal muscle were produced and characterized. Using these antibodies it was possible to demonstrate that skeletal muscles of varying fiber type express different isoforms of this protein and that in the posterior latissimus dorsi muscle both isoforms are coexpressed in the same myofiber. Since both isoforms were present in all sarcomeres, it was feasible to test whether the 2 isoforms codistributed in the same 42-nm repeat within the A-band, thereby establishing a minimum number of C-proteins per repeat in the thick filaments. The ultrastructural localization of C-protein in myofibers from 3 muscle types of the chicken using these same McAb was described. Although C-protein was present in a 43-nm repeat along the filaments in all 3 muscles, there were marked differences in the absolute number and position occupied by the different isoforms. Since McAb MF-1 and ALD-66 decorated the same 43-nm repeats in the A-bands of the posterior latissimus dorsal muscle, evidently at least 2 C-proteins can colocalize at binding sites 43 nm apart along thick filaments of this muscle.