Myosin Isozymes in Developing Chicken Muscles

Abstract

There is now general agreement among several laboratories that a minimum of three classes of myosin isozymes appear sequentially during the course of muscle development (56,381,386, 551). These classes include embryonic, neonatal and adult myosin. Even though the primary structure of these myosins is different (552,553), their overall size and shape remains unchanged (Figure 85B). A more difficult, and largely unresolved problem is the functional significance of this polymorphism. It is widely assumed that myosin isozymes have different enzymatic properties which can be related to the speed of shortening of the muscle from which the myosin is derived (554). Here it will be shown that this correlation does not necessarily apply to developing muscles, and that alternative explanations for myosin diversity need to be found.