Chicken cardiac muscle myofibrils lack a visible M-line. Antibodies against chicken breast muscle M-protein, an M-line component with Mr= 165 000, were used to demonstrate the presence of a similar protein in chicken heart muscle. The immunoreplica technique showed the heart protein to have about the same molecular weight as the breast muscle M-protein on polyacrylamide slab gels in the presence of sodium dodecyl sulfate (SDS). Positive staining within the H-zone was observed when the indirect immunofluorescence technique was used to localize the M-protein in isolated heart myofibrils. This result was confirmed by electron microscopic investigations on longitudinal sections of antibody-incubated heart muscle fiber bundles showing the antibody against M-protein to be bound within a region corresponding to the M-line region of breast muscle myofibrils. © 1979.
Strehler, E. E., Pelloni, G., Heizmann, C. W., & Eppenberger, H. M. (1979). M-protein in chicken cardiac muscle. Experimental Cell Research, 124(1), 39–45. https://doi.org/10.1016/0014-4827(79)90255-6