Comparison of chitinase isozymes from yam tuber - Enzymatic factor controlling the lytic activity of chitinases

To evaluate the anti-pathogen activity of chitinases, we developed a new me thod for measuring the lytic activity, and investigated the correlation of the lytic activity with the enzymatic properties by using four chitinase is ozymes, Chitinases E, F, H1 and G, which had been purified from yam tubers by column chromatography. Chitinases E, F and H1 had high lytic activity ag ainst the plant pathogen, Fusarium oxysporum, but Chitinase G did not. Chit inase E, which is the family 19 chitinase, was similar to Chitinases F and G in its antigenecity, but not to Chitinase H1 or H2. Chitinases H1 and H2 were recognized by the anti-Bombyx mori chitinase antibody, suggesting that Chitinases H1 and H2 are family 18 chitinases like B. mori chitinases. Chi tinases E, F and H1 had two optimum pH ranges of 3-4 and 7.5-9 toward glyco lchitin, but Chitinase G had only one optimum pH value of 5. Chitinases E, F and H1 had higher affinity to the polymer substrate, glycolchitin, than C hitinase G. These results suggest that the lytic activity of plant chitinas es may be related to the chitin affinity and probably to the characteristic optimum pH value, or two values, but not related to its classification. Th e correlation of the lytic activity of a chitinase isozyme with its elicito r specificity is also discussed.