PLG-007 and Its Active Component Galactomannan-α Competitively Inhibit Enzymes That Hydrolyze Glucose Polymers

PLG-007 is a developmental therapeutic compound that has been clinically shown to reduce the magnitude of postprandial glucose excursions and has the potential to be an adjunct treatment for diabetes and inflammatory-related diseases. The present investigation is aimed at understanding the molecular mechanism of action of PLG-007 and its galactomannan (GM) components GMα and GMβ (in a 1:4 mass ratio, respectively) on enzyme (i.e., α-amylase, maltase, and lactase) hydrolysis of glucose polymers using colorimetric assays and (13)C HSQC NMR spectroscopy. The starch–iodine colorimetric assay indicated that GMα strongly inhibits α-amylase activity (~16-fold more potent than GMβ) and thus is the primary active component in PLG-007. (13)C HSQC experiments, used to follow the α-amylase-mediated hydrolysis of starch and amylopectin, further demonstrate the α-amylase inhibitory effect of GMα via α-amylase-mediated hydrolysis of starch and amylopectin. Maltohexaose (MT6) was used to circumvent the relative kinetic complexity of starch/amylopectin degradation in Michaelis–Menten analyses. The V(max), K(M), and K(i) parameters were determined using peak volume integrals from (13)C HSQC NMR spectra. In the presence of PLG-007 with α-amylase and MT6, the increase in K(M) from 7.5 ± 0.6 × 10(−3) M (control) to 21 ± 1.4 × 10(−3) M, with no significant change in V(max), indicates that PLG-007 is a competitive inhibitor of α-amylase. Using K(M) values, K(i) was estimated to be 2.1 ± 0.9 × 10(−6) M; however, the microscopic K(i) value of GMα is expected to be larger as the binding stoichiometry is likely to be greater than 1:1. Colorimetric assays also demonstrated that GMα is a competitive inhibitor of the enzymes maltase and lactase. Overall, this study provides insight as to how PLG-007 (GMα) is likely to function in vivo.