Solubilisation of myosin in a solution of low ionic strength l-histidine: Significance of the imidazole ring

•l-Histidine (His), imidazole (Imi) and l-carnosine (Car) increased solubility of myosin in low ionic strength solution.•His, Imi and Car gave myosin suspensions with small particle size species.•His, Imi and Car increased the absolute zeta potential of myosin suspension.•His, Imi and Car induced conformational changes of soluble myosin.•Imidazole ring was the significant constituent in His for solubilising myosin.

Myosin, a major muscle protein, can be solubilised in a low ionic strength solution containing l-histidine (His). To elucidate which chemical constituents in His are responsible for this solubilisation, we investigated the effects of 5 mM His, imidazole (Imi), l-α-alanine (Ala), 1-methyl-l-histidine (M-his) and l-carnosine (Car) on particle properties of myosin suspensions and conformational characteristics of soluble myosin at low ionic strength (1 mM KCl, pH 7.5). His, Imi and Car, each containing an imidazole ring, were able to induce a myosin suspension, which had small particle size species and high absolute zeta potential, thus increasing the solubility of myosin. His, Imi and Car affected the tertiary structure and decreased the α-helix content of soluble myosin. Therefore, the imidazole ring of His appeared to be the significant chemical constituent in solubilising myosin at low ionic strength solution, presumably by affecting its secondary structure.