Abstract:The structural variations in the subunits of arachin and conarachin under acidic conditions were investigated by zeta potential, intrinsic fluorescence spectroscopy, average hydrodynamic diameter analyses, sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE), and solubility. According to the electrophoretic analysis, the 40.5 ku, 37.5 ku, 35.5 ku, and 27 ku subunits of arachin were acid-hydrolyzed into a new 32.86 ± 0.10 ku band; while the levels of the 22 ku and 15 ku bands increased. When the pH was <2.0, the acid hydrolysis of arachin was totally inhibited by the electrostatic shielding that occurs at extreme pH. In the pH range of 1.0~3.0, the 61 ku subunit of conarachin was acid-hydrolyzed into 36.95 ± 0.50, 25.14 ± 1.86, 18.98 ± 0.78, and 17.37±1.17 ku bands. Further studies indicated that both arachin and conarachin unfolded under acidic conditions, and the particle size increased; when the pH values were in the range of 2.0~3.0, the zeta potential and solubility were relatively higher than that in other pH ranges. In the pH 2.0~3.0 range, the maximum emission wavelength in the fluorescence spectra of arachin was red-shifted as compared to that under neutral conditions; and the amplitude of this redshift was greater than that of conarachin, indicating that the degree of conarachin unfolding was lesser than that of arachin. In sum, the degrees of hydrolysis and structural changes of conarachin were lesser than those of arachin, indicating that conarachin is less acid-sensitive than arachin.
