Characterization of acidic chitinases from culture medium of sweet orange callus tissue

Two acidic chitinases (E.C. 3.2.1.14) were purified from embryogenic Citrus sinensis L. Osbeck cv. Hamlin, callus tissue culture medium. The two proteins showed chitinase and chitosanase activity but no lysozyme activity. The enzyme activities decreased with decreasing acetylation of the chitin substrate. Both hydrolases were endochitinases and showed distinct differences in their digestion pattern towards chitin substrates of varying lengths. Hydrolysis of a chitin hexamer substrate with ACHCM-1 resulted only in dimeric products whereas ACHCM-2 released chitin dimers and trimers. The ACHCM-1 chitinase showed a Mr of 28,000 and a pI of 5.8 (determined by chromatofocusing) whereas the ACHCM-2 protein was characterized by a M(r) of 25,000 and a pI of 5.0. The N-terminal sequences of both proteins were similar and showed homology to the class III chitinases. The two chitinases showed distinct differences in their serological characteristics.