Troponin-T and glyceraldehyde-3-phosphate dehydrogenase share a common antigenic determinant

A 37 kDa protein in extracts of bovine aorta and equine platelets was observed on SDS-polyacrylamide gel electrophoretograms to react with polyclonal and monoclonal antibodies to rabbit skeletal troponin-T (TnT) by immunoblotting. Following purification by precipitation at pH 4.6 and several ion-exchange chromatographic steps, it has been identified as glyceraldehyde-3-phosphate dehydrogenase (G3PD) by amino acid analyses and NH2-terminal sequencing. By ELISA, the anti-troponin-T monoclonal antibody reacted with rabbit skeletal G3PD appreciably but 120-fold less specifically than with TnT. A cyanogen bromide fragment (CB2) of TnT (residues 71-151) reacted with the monoclonal antibody nearly as well as intact TnT. This cross-reactivity between G3PD and TnT can be ascribed to a weak homology in the amino acid sequences of the two proteins between residues 72-80 of TnT and residues 157-165 of G3PD. Other regions of limited sequence similarity in the two proteins are also present. We conclude that the identification of diffuse cytoplasmic indirect immunofluorescent staining observed with a monoclonal anti-TnT antibody in chicken gizzard muscle is probably attributable to cross-reactivity with G3PD.