-Glucosidase isozymes and the labellar sugar receptor of the blowfly

Some properties of four types of the soluble α-glucosidase, especially of P-II α-glucosidase of Amakawa and others, from the labella of the blowfly were examined and compared with those of the sugar receptor of the blowfly. Tris (hydroxymethyl) aminomethane inhibited four types of α-glucosidase and the electrical response of the sugar receptor, all in a competitive manner, but the inhibition constants (K_i) for these glucosidases were more than 150 times smaller than that for the sugar receptor. l-Serine inhibited α-glucosidases competitively, but the inhibition for the sugar receptor was not clear. The effects of cations and amino acids on α-glucosidases were also examined in relation to those on the sugar receptor.