Secretion of basic and acidic chitinases from salt‐adapted and ‐unadapted winged bean cells

Abstract

Six specific proteins are secreted from salt‐adapted winged bean (Psophocarpus tetragonolobus) cells. A protein, designated S AP3, with molecular mass of 37 000 was secreted abundantly by suspension cultures of winged bean callus adapted to 0.5% (86 mM) or 1.0% (171 mM) NaCl. When the amino acid sequence of the amino‐terminal part (16 amino acid residues) of SAP3 was determined, a significant homology was found between the amino‐terminal amino acid sequence of SAP3 and that of basic chitinase from kidney bean, Arabidopsis, tobacco and pumpkin. SAP3 had chitinase activity, suggesting that basic chitinase is secreted specifically from salt‐adapted winged bean cells. A protein with molecular mass of 29000 was exclusively secreted into the culture medium at the later stage (20–30 days) of both salt‐adapted and ‐unadapted cultures. The protein was purified from the medium at day 30. One‐step ammonium sulfate fractionation was sufficient for purification to homogeneity. The protein had chitinase activity. The amino‐terminal amino acid sequence (17 amino acid residues) of the protein suggested that it was acidic chitinase. Thus, acidic chitinase with a molecular mass of 29000 is exclusively secreted at the later stage of culture of salt‐adapted and ‐unadapted winged bean cells, in contrast to pumpkin (Cucurbita) cell suspension cultures where basic chitinase with a molecular mass of 32 000 is secreted abundantly at the early culture stage.