Kinetic investigation of a new inhibitor for human salivary α-amylase

This study is the first report on the effectiveness and specificity of α-acarviosinyl-(1 → 4)-α-d-glucopyranosyl-(1 → 6)-d-glucopyranosylidene-spiro-thiohydantoin (PTS-G-TH) inhibitor on the 2-chloro-4-nitrophenyl-4-O-β-d-galactopyranosyl-maltoside (GalG2CNP) and amylose hydrolysis catalysed by human salivary α-amylase (HSA). Synthesis of PTS-G-TH was carried out by transglycosylation using acarbose as donor and glucopyranosylidene-spiro-thiohydantoin (G-TH) as acceptor. This new compound was found to be a much more efficient HSA inhibitor than G-TH. The inhibition is a mixed-noncompetitive type on both substrates and only one molecule of inhibitor binds to the enzyme. Kinetic constants calculated from secondary plots are in micromolar range. Values of KEI and KESI are very similar in the presence of GalG2CNP substrate; 0.19 and 0.24 μM, respectively. Significant difference can be found for KEI and KESI using amylose as substrate; 8.45 and 0.5 μM, respectively. These values indicate that inhibition is rather uncompetitive than competitive related to amylose hydrolysis.