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 prot eins showed chitinase and chitosanase activity but no lysozyme activity The enzyme activities decreased with decreasing acetylation of the chitin subs trate. Both hydrolases were endochitinases and showed distinct differences in their digestion pattern towards chitin substrates of varying lengths. Hy drolysis of a chitin hexamer substrate with ACHCM-1 resulted only in dimeri c products whereas ACHCM-2 released chitin dimers and trimers. The ACHCM-1 chitinase showed a M-r of 28,000 and a pI of 5.8 (determined by chromatofoc using) 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 sh owed homology to the class III chitinases. The two chitinases showed distin ct differences in their serological characteristics.