Difference UV-Absorption Spectrum of Scallop Adductor Myosin Induced by ATP1

A difference UV-absorption spectrum induced by ATP was observed with scallop myosins purified from both striated and smooth adductor muscles. The difference spectra showed a positive peak at 289 nm with a shoulder around 295 run, and two small negative troughs around 280 run. Tryptophanyl movement similar to that in rabbit skeletal myosin is indi-cated. Some tyrosyl movements in scallop myosins, however, may be in the opposite direction. Scallop has two kinds of adductor containing different types of muscle, one striated and the other smooth. The smaller adductor containing smooth muscle is known to adopt a "catch " state. Regula-tion of molluscan muscle by calcium ions is me-diated by a myosin-linked system (1) which is different from the actin-linked regulatory system of vertebrate skeletal muscle (2). In spite of these interesting properties of scallop muscles, com-parisons of the physico-chemical properties of myosin obtained from the two kinds of adductors, or of the properties of scallop myosins and of rabbit myosin are still not complete. We have examined scallop myosins purified from both adductor muscles to determine whether a difference UV-absorption spectrum is induced by the addition of ATP, as is the case with skeleta