Study on Polysaccharide by the Fluorescence Method. II. Micro-Brownian Motion and Conformational Change of Amylose in Aqueous Solution

Abstract

The segmental motion of amylose in aqueous solution and the conformational transition with temperature and pH were studied by the fluorescence polarization method. We prepared two types of fluorescent conjugates of amylose: amylose conjugated with fluorescein randomly throughout chain (F-Amylose) and amylose conjugated locally on a terminal segment (t-F-Amylose). The value of the rotational relaxation time for t-F-Amylose was much smaller than that for F-Amylose. This result suggests that a terminal segment undergoes a more rapid micro-Brownian motion than interior segments. Polarization curves of these conjugates gradually departed from the Perrin equation when the temperature was raised. F-Amylose showed a gradual departure above 45°C but t-F-Amylose showed a departure at room temperature. This indicates that the conformational transition occurs first in terminal segments and then extends to the interior segments with increasing temperature. The effect of pH on the polarization was also examined. When measured as a function of pH, fluorescence depolarization increased pronouncedly in the alkaline region. In contrast to changing temperature, depolarization began to increase at the same pH for the two amylose conjugates.