Abstract
The surface accessibility of mobile domains of rabbit fast muscle myosin subfragment-1 isoenzymes (subfragment-1(A1), (A2)) influenced by interaction with actin has been investigated by proton magnetic resonance spectroscopy using the soluble paramagnetic reagents Cr(CN) 6 3−, Fe(CN) 6 3−, Mn 2+ and the Gd 3+ salt of 1,4,7,10-tetraazacyclododecane- N, N′, N″, N″'-tetraacetic acid as probes. Anionic probes interact principally with lysine residues disposed close to other non-charged sidechains in both isoenzymes. Additional resonances in subfragment-1(A1) not present in subfragment-1(A2) are also observed to be affected, notably the sharp signal at 3.23 ppm which derives from a -N + (CH 3) 3 group found in the N-terminal segment of the A1 light chain, showing that this domain of interaction with actin (Prince et at. (1981) Eur. J. Biochem. 121, 213–219) is situated at a surface location. Different probes identify a heterogeneity in the location and function of mobile sidechains. These results suggest a configurational lability in the various parts of the myosin head, differentially constrained upon interaction with actin and consistent with a structure composed of relatively rigid domains linked by more flexible regions.
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