Using SDS-PAGE, three isoforms were separated for all three species. Western blotting confirmed their nature as MHC I, MHC IIa and MHC IIx (Fig. 3). Both MHC I and IIa of the felids migrated similarly on the gel to that of human muscle. However, the MHC IIx differed significantly, even between the two felids. According to the migratory size, the lion expressed the smallest MHC IIx isoform, followed by that of caracal and human (Fig. 3A). A different amino acid sequence, or a lack thereof, may contribute to this size difference. It is unclear what the effect of this size difference might have on the overall contractility of these fibers.