Aleppo tannin: structural analysis and salivary amylase inhibition

The effectiveness and specificity of a tannin inhibition on human salivary amylase (HSA) catalyzed hydrolysis was studied using 2-chloro-4-nitrophenyl 4-O-beta-D-galactopyranosyl-alpha-maltoside (GalG(2)-CNP) and amylose substrates. Aleppo tannin was isolated from the gall nut of Aleppo oak. This tannin is a gallotannin, in which glucose is esterified with gallic acids. This is the first kinetic report, which details the inhibitory effects of this compound on HSA. A mixed non-competitive type inhibition has been observed on both substrates. The extent of inhibition is markedly dependent on the substrate-type. Kinetic constants were calculated from Lineweaver-Burk secondary plots for GalG(2)-CNP (K(EI) 0.82 microg mL(-1), K(ESI) 3.3 microg mL(-1)). This indicates a 1:1 binding ratio of inhibitor-enzyme and/or inhibitor-enzyme-substrate complex. When amylose was the substrate the binding ratio of inhibitor to enzyme-substrate complex was found to be 2:1, with the binding constants of K(EI) 17.4 microg mL(-1), K(ESI) 14.9 microg mL(-1), K(ESI(2)) 9.6 microg mL(-1). Presumably, the tannin inhibitor can bind not only to HSA, but to the amylose substrate, as well. Kinetic data suggest that Aleppo tannin is a more efficient amylase inhibitor than the recently studied other tannin with quinic acid core (GalG(2)-CNP: K(EI) 9.0 microg mL(-1), K(ESI) 47.9 microg mL(-1)).