3 EXTRACELLULAR CHITINASES IN SUSPENSION-CULTURED RICE CELLS ELICITEDBY N-ACETYLCHITOOLIGOSACCHARIDES

In rice suspension culture, a large part (about 90% of total activity in the culture) of the chitinase activity was found in the medium, Two extracellular chitinases (which we named RCH-A and -B) were separated from the cell suspension by DEAE-cellulofine column chromatography. W hen cells ere treated with N-acetylehitooligosaccharides (chitin oligo saccharides) for 3 days, extracellular chitinase activity increased ab out 3-fold over the control culture, After the treatment, another extr acellular chitinase (named RCH-C) appeared in addition to increases in the levels of RCH-A and -B, Partial amino acid sequences of these enz ymes indicated that RCH-A (33.5 kDa) and -B (33 kDa) were class Tb chi tinases but RCH-C (27 kDa) was a class III chitinase, RCH-A and -B wer e capable of actively degrading water-insoluble chitin with high affin ities, while RCH-C had less affinity for the substrate, However, when a water-soluble chitin derivative, 6-O-hydroxyethylchitin (glycolchiti n) was used, RCH-C as well as RCH-A and -B degraded actively with a hi gh affinity, A synergistic effect was observed when these three chitin ases acted simultaneously in the hydrolysis of chitin.