3.3. Kinetic analysis of α-glucosidase inhibition by C1 and C2
C1 and C2 were selected for further kinetic inhibition experiments
against yeast α-glucosidase since it wielded a remarkable inhibitory
activity. For kinetic studies, enzyme was incubated with designated
concentrations of substrate pNPG in the absence (control) or presence
of IC20, IC40 and IC60 inhibitory concentrations of C1 and C2. Mode of inhibition, [Km] and [Vmax] values were determined by graphical means
using Lineweaver–Burk plots. Lineweaver–Burk plots revealed that the
intersecting point for different concentrations of C1 (Fig. 2A) and C2
(Fig. 2B) arises from the same x-intercept as uninhibited enzyme
other than diverse slopes and y-intercepts. With the increasing concentrations of C1 and C2, both the slope and the vertical axis intercept
increased, whereas, the horizontal axis intercept (−1/ Km) remained
the same. The kinetic results established that C1 and C2 retarded
the maximum velocity (Vmax) of the reaction (with increasing concentrations) catalysed by α-glucosidase without much change in Km values
(Table 2). These results indicated that the mechanism of α-glucosidase
inhibition was reversible, corresponding to the classical pattern of noncompetitive inhibition. The inhibitory constant (Ki), determined from
Dixon plots for α-glucosidase was 1.61 and 2.87 μg of C1 and C2
respectively.