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

VIII. Thiols of Myosin

Abstract

Myosin has 2 mol of the most reactive thiol, named SH₁. 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 SH₁ 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 SH₁ was about twice compared with that of NEM, the most reactive and selective reagent for SH₁ 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 8M urea.
This outstanding feature of SH₁ modification with TNB was discussed in terms of affinity labeling by interaction with an aromatic amino acid near SH₁.