Electron microscopic studies of myosin molecules from chicken gizzard muscle I: the formation of the intramolecular loop in the myosin tail.

The ATP-induced disassembled molecules of chicken gizzard myosin from "thick filaments" have been examined in the electron microscope using the rotary-shadowing technique and have been compared with the myosin molecules disassembled by high concentrations of ammonium acetate without ATP. Both myosin molecules consisted of two globular heads and a long tail. However, two remarkable differences between these myosin molecules were observed: 1. Most of the myosin molecules disassembled by ATP had intramolecular hairpin "loops" in the tails. The length of the hairpin loop was about 510 A and that of the remaining part of the tail was about 600 A. On the other hand, no myosin molecules disassembled by ammonium acetate had the intramolecular loop in the tail. 2. The two globular heads of myosin molecules disassembled by ATP tended to bend back towards the tail, but those of the myosin molecules disassembled by ammonium acetate tended to bend forwards.