Evidence for distinct phosphorylatable myosin light chains in avian heart and slow skeletal muscle

In mammalian organisms the regulatory or phosphorylatable myosin light chains in heart and slow skeletal muscle have been shown to be identical and presumable constitute the product of a single gene. We analyzed the expression of the avian cardiac myosin light chain (MLC) 2-A in heart and slow skeletal muscle by a combination of experimental approaches, e.g., two-dimensional gel electrophoresis of the protein and hybridization of mRNA to specific MLC 2-A sequences cloned from chicken. The investigations have indicated that, unlike in mammals, in avian organisms the phosphorylatable myosin light chains from heart and slow skeletal muscle are distinct proteins and therefore products of different genes. The expression of MLC 2-A is restricted to the myocardium and no evidence was found that it is shared with slow skeletal muscle.