Local structural changes in tropomyosin detected by a trypsin-probe method.

Structural changes in tropomyosin from rabbit skeletal muscle were studied by the tryptic digestion method, which is an application of the quantitative enzyme-probe method recently developed by Ueno and Harrington [Ueno, H., & Harrington, W.F. (1984) J. Mol. Biol. 173, 35-61]. Effects of ionic strength, temperature, and an interchain disulfide bond at Cys-190 on the structure of tropomyosin were examined. A region of high susceptibility to trypsin was found to be localized in the middle portion of the molecule, and its susceptibility increased on lowering ionic strength and/or raising temperature. With the introduction of a disulfide bond at Cys-190, cleavage on the N-terminal side of Cys-190 was accelerated. The results suggest that skeletal muscle tropomyosin is flexible in the middle of the molecule in contrast to the flanking N- and C-terminal trypsin-resistant segments.