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Thielavins A, J and K: alpha-glucosidase inhibitors from MEXU 27095, an endophytic fungus from Hintonia latiflora
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Bioassay-guided fractionation of the bio-active organic extract obtained from solid-media culture of MEXU 27095, an endophytic fungus isolated from the Mexican medicinal plant Hintonia latiflora (Rubiaceae), led to separation of three tridepsides which were identified as thielavins A, J and K. All three compounds inhibited Saccharomyces cerevisieae a-glucosidase (aGHY) in a concentration-dependent manner with IC50 values of 23.8, 15.8, and 22.1 lM, respectively. Their inhibitory action was higher than that of acarbose (IC50 = 545 lM), used as a positive control. Kinetic analysis established that the three compounds acted as non-competitive inhibitors with ki values of 27.8, 66.2 and 55.4 lM, respectively (a = 1.0, 1.2, 0.7, respectively); acarbose behaved as competitive inhibitor with a ki value of 156.1 lM. Thielavin J inhibited the activity of a-glucosidase from Bacillus stearothermophilus (aGHBs) with an IC50 of 30.5 lM, being less active than acarbose (IC50 = 0. 015 lM); in this case, compound (2) (ki = 20.0 lM and a = 2.9) and acarbose (ki = 0.008 lM and a = 1.9) behaved as non-competitive inhibitors. Docking analysis predicted that all three thielavins and acarbose bind to homologated aGHBs and to aGHY (PDB: 3A4A) in a pocket close to the catalytic site for maltose and isomaltose, respectively. The a-glucosidase inhibitory properties of thielavin K (3) were corroborated in vivo since it induced a noted antihyperglycemic action during an oral sucrose tolerance test (3.1, 10.0 and 31.6 mg/kg) in normal and nicotinamide–streptozotocin diabetic mice. In addition, at a dose of 10 mg/kg, it provoked a moderate hypoglycemic activity in diabetic mice.
Anthony E Glenn
inhibitory concentration 50
Phytochemistry 2013 v.94
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