This chapter discusses the sulfhydryl modification and labeling of myosin. Two sulfhydryl groups, the SH1 and SH2 groups located on the heavy chain of subfragment-1 of myosin, have been extensively studied because their modification was found to affect dramatically the ATPase activities of myosin. The sulfhydryl reagents differ in their reactivity toward the SH1 groups on myosin. Consequently, for each reagent it is desirable to establish optimal conditions for specific labeling of the SH1 groups. This can be done by following the changes in myosin ATPases as a function of increasing incorporation of the reagent. The goal in such experiments is to find reaction conditions under which incorporation of 1 mol of reagent per mole of myosin head results in maximum inhibition of K(EDTA)-ATPase and maximum activation of the Ca- ATPase. These changes in myosin activity are indicative of SH1 modification. The assignment of the modification site on the basis of ATPase properties alone is purely inferential. It is based on the previous identification of the modified peptides in reactions of myosin with NEM and iodoacetamide. Addtionally, specific and relatively rapid modification of the SH1 groups on myosin can be achieved by allowing N-ethylmaleimide and maleimide-based reagents to react with myosin, S-l, or heavy meromyosin. © 1982, Elsevier Inc. All rights reserved.
Reisler, E. (1982). Sulfhydryl Modification and Labeling of Myosin. Methods in Enzymology, 85(C), 84–93. https://doi.org/10.1016/0076-6879(82)85012-X