Paramyosin from arthropod cross-striated muscle

Abstract

1. 1. Paramyosin was isolated and purified from acetone powders and fresh cross-striated muscle of Limulus polyphemus, the horseshoe crab. The purified protein exhibited a single peak in the ultracentrifuge and a single band in disc-gel electrophoresis. 2. 2. Limulus paramyosin contained a high content a Asp and Glu comparable to other paramyosins and from optical rotatory dispersion and circular dichroism measurements appeared to be about 80% α-helical. 3. 3. Only the PI 2 5 and DIII forms of paracrystals have been obtained but these gave a major repeat pattern averaging 726 Å; comparable Mercenaria mercenaria paracrystals gave, in our hands, a major period of 723 Å. 4. 4. An intrinsic viscosity of 1·99 and 2·38 dl/g for Mercenaria and paramyosins, respectively, indicates different sized molecules. This agrees with the differences in S 20,w 0 for the two, 3·40 and 4·07 S, Mercenaria and Limulus respectively, as well as with the different molecular weights, 208,000 Daltons ( Mercenaria) and 284,000 Daltons ( Limulus) determined by extrapolation of Archibald and meniscus electrophoresis of the two different paramyosins previously incubated in 8 M urea also indicate a larger chain weight for the Limulus paramyosin than for the Mercenaria.