Achacin is an antibacterial glycoprotein puri¢ed from the mucus of the giant snail, Achatina fulica Fe ¤russac, as a humoral defense factor. We showed that achacin has L-amino acid oxidase activity and can generate cytotoxic H 2 O 2 ; however, the concentration of H 2 O 2 was not su⁄cient to kill bacteria. The antibacterial activity of achacin was inhibited by various H 2 O 2 scavengers. Immunochemical analysis revealed that achacin was preferentially bound to growth-phase bacteria, accounting for the important role in growth-phase-dependent antibacterial activity of achacin. Achacin may act as an important defense molecule against invading bacteria.

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T1R2/T1R3 belongs to G protein coupled receptors, which recognizes diverse natural and synthetic sweeteners. A novel class of positive allosteric modulators (PAMs) of T1R2/T1R3 was identified through high-throughput screening campaign. Comparing the structure of the potent compound with previously known PAM, we classified the structure of known PAM into three parts, defined as "head", "linker", and "tail". We then investigated the linker−tail structure. It was suggested by molecular docking models of T1R2/T1R3 that an amine that we introduced in the tail was the key for interaction with the receptor binding pocket. We thus synthesized various molecules and found unnatural tripeptide-PAMs, which potently enhance the sweetness of sucrose in sensory evaluation tests.