Fluorescence Intensity and UV Absorption Changes Accompanying Dissociation and Association of Regulatory Light Chain of Scallop Adductor Myosin1

1. Dissociation and association of regulatory light chains of scallop myosin were found to be accompanied by changes in the fluorescence intensity and in the UV absorption spectrum. 2. The changes in the two optical properties of scallop myosin and the dissociation and association of regulatory light chains were studied as a function of the magne-sium and calcium concentrations. The results thus obtained suggested that there are two different types of attachment between regulatory light chains and "desen-sitized " myosin; one type is a calcium-specific attachment, and the other type of attachment can be mediated by either calcium or magnesium ions. 3. These changes in the optical properties of scallop myosin were distinguishable from those induced by Mg-ATP; for example, with "desensitized " scallop myosin, the former changes were not observed but the latter were. Nucleotide-induced change in the UV absorption isolated from scallop adductor myosin was not spectrum of rabbit skeletal myosin is known to altered upon addition of calcium. Chantler and occur (1), and calcium-induced change in fluores- Szent-Gyorgyi (5) reported that no change in th