SummaryThe inhibitory activity of six groups of flavonoids against yeast and rat small intestinal ␣ -glucosidases and porcine pancreatic ␣ -amylase was compared, and chemical structures of flavonoids responsible for the inhibitory activity were evaluated. Yeast ␣ -glucosidase was potently inhibited by the anthocyanidin, isoflavone and flavonol groups with the IC 50 values less than 15 M . The following structures enhanced the inhibitory activity: the unsaturated C ring, 3-OH, 4-CO, the linkage of the B ring at the 3 position, and the hydroxyl substitution on the B ring. Rat small intestinal ␣ -glucosidase was weakly inhibited by many flavonoids, and slightly by the anthocyanidin and isoflavone groups. 3-OH and the hydroxyl substitution on the B ring increased the inhibitory activity. In porcine pancreatic ␣ -amylase, luteolin, myricetin and quercetin were potent inhibitors with the IC 50 values less than 500 M . The 2,3-double bond, 5-OH, the linkage of the B ring at the 3 position, and the hydroxyl substitution on the B ring enhanced the inhibitory activity, while 3-OH reduced it.

Novel antimicrobial peptides (AMP), designated Fa-AMP1 and Fa-AMP2, were purified from the seeds of buckwheat (Fagopyrum esculentum Moench.) by gel filtration on Sephadex G75, ion-exchange HPLC on SP COSMOGEL, and reverse-phase HPLC. They were basic peptides having isoelectric points of over 10. Fa-AMP1 and Fa-AMP2 had molecular masses of 3,879 Da and 3,906 Da on MALDI-TOF MS analysis, and their extinction coefficients in 1% aqueous solutions at 280 nm were 42.8 and 38.9, respectively. Half of all amino acid residues of Fa-AMP1 and Fa-AMP2 were cysteine and glycine, and they had continuous sequences of cysteine and glycine. The concentrations of peptides required for 50% inhibition (IC50) of the growth of plant pathogenic fungi, and Gram-positive and -negative bacteria were 11 to 36 microg/ml. The structural and antimicrobial characteristics of Fa-AMPs indicated that they are a novel type of antimicrobial peptides belonging to a plant defensin family.

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Antimicrobial peptides are important components of the host innate immune responses by exerting broad-spectrum microbicidal activity against pathogenic microbes. Cy-AMP1 found in the cycad (Cycas revoluta) seeds has chitin-binding ability, and the chitin-binding domain was conserved in knottin-type and hevein-type antimicrobial peptides. The recombinant Cy-AMP1 was expressed in Escherichia coli and purified to study the role of chitin-binding domain. The mutants of Cy-AMP1 lost chitin-binding ability completely, and its antifungal activity was markedly decreased in comparison with native Cy-AMP1. However, the antimicrobial activities of the mutant peptides are nearly identical to that of native one. It was suggested that the chitin-binding domain plays an essential role in antifungal, but not antimicrobial, activity of Cy-AMP1.

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