抄録
1. Conjugation of myosin A with 1-dimethylaminonaphthalene-5-sulfonyl chloride (DNS) produced a quenching of the tryptophan fluorescence depending on the degree of labeling. It was shown that the degrees of quenching of the ultraviolet fluorescence by labeling with the dye in different proteins were almost of the same order of magnitude if the degree of labeling is expressed as “moles dye per mole tryptophan”.
2. The ultraviolet fluorescence of DNS-labeled myosin A showed a significant quenching in the pH region in which “normal” tyrosine ionize. The quenching of the visible fluorescence excited by the irradiation in the tryptophan region (285mμ) approximately paralleled the ionization zone of “abnormal” tyrosine. The DNS fluorescence excited at 330mμ was slightly enhanced in these alkaline pH region. In the presence of ethanol, these alkaline quenching curves were shifted slightly to lower pH values.
Urea decreased the ultraviolet and the visible fluorescence at pH's below about 10. However, it reduced the alkaline quenching of both fluorescence intensities and enhanced the visible fluorescence excited at 330mμ in this alkaline pH region.
The visible fluorescence intensity excited at 330mμ decreased more extensively than that excited at 285mμ at pH 6.
3. The time-dependence of the fluorescence intensities was studied after the addition of dioxane, ethanol, and urea. Furthermore, the effects of urea and guanidine hydrochloride on the intensities were measured at different concentrations of the reagents.
The results obtained showed that the measurements of the fluorescence intensities of both the tryptophanyl residues of myosin A and DNS attached to the enzyme provides a useful means to monitor the structural transitions of the protein.
