The extent of amino-terminal heterogeneity in rabbit fast skeletal muscle troponin T.

The extent and nature of fast troponin T (TnT) heterogeneity has been assessed in rabbit skeletal muscle. Previous studies identified two major fast TnT species (TnT1f and TnT2f), in the fast white muscle erector spinae, differing in their N-terminal cyanogen bromide (CNBr) fragments. Here a monoclonal antibody that recognizes a conserved region of TnT was used to characterize two additional TnT species (TnT3f and TnT4f) in the epaxial and limb musculature and a minor species (TnTcf) in craniofacial muscles. A combination of CNBr peptide mapping, immunoblotting and specific labelling of the N-terminus shows that these TnT species also differ in their N-terminal region. This observation is consistent with cDNA studies that predicted the N-terminal region is hypervariable. One additional species, a variant of TnT2f present in the tongue, was identified by two-dimensional gel electrophoresis. The limited number of TnT variants indicates that the full potential for heterogeneity inferred from the cDNA studies is not realized. This conclusion is supported by immunoblot analysis with a monoclonal antibody that recognizes an epitope in the hypervariable N-terminal region which is present in all variants of TnT1f and TnT2f but absent from the lower molecular weight species TnT3f and TnT4f.