Selective Modification of Myosin SH1 with 1,2,4-Trinitrobenzene1

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Abstract
Myosin has 2 mol of the most reactive thiol, named SH 1 . 1,2,4-Trinitrobenzene (TNB), a novel dinitrophenyl(DNP)ating reagent [Takahashi et al . (1983) Chem. Lett . 1445–1448], was found to react only with SH 1 without any other amino acid residues in myosin under the conditions used. Its reaction with myosin SH1 was about 30 times faster than that with N -acetylcysteine (NAC). The reaction rate of TNB with SH 1 was about twice compared with that of NEM, the most reactive and selective reagent for SH 1 so far found, although its rate with NAC was only one sixtieth that of NEM. As to the λ max of the absorption spectrum of SH1-DNP- myosin, a large red shift of as much as 20 nm was observed compared with low molecular S-DNP derivatives. This red shift disappeared in 8 M urea. This outstanding feature of SH 1 modification with TNB was discussed in terms of affinity labeling by interaction with an aromatic amino acid near SH 1 .

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