Fungi, such as Coccidioides immitis, also possess degradative chitinases related to their role as detritivores and also to their potential as arthropod pathogens.

Expression is mediated by the NPR1 gene and the salicylic acid pathway, both involved in resistance to fungal and insect attack.

[10] Chitinases were also classified based on the amino acid sequences, as that would be more helpful in understanding the evolutionary relationships of these enzymes to each other.

[14] Both families 18 and 19 consists of endochitinases from a variety of different organisms, including viruses, bacteria, fungi, insect, and plants.

Characteristics that determined the classes of chitinases were the N-terminal sequence, localization of the enzyme, isoelectric pH, signal peptide, and inducers.

[13] Class I chitinases had a cysteine-rich N-terminal, leucine- or valine-rich signal peptide, and vacuolar localization.

[17] Many mammals can digest chitin and the specific chitinase levels in vertebrate species are adapted to their feeding behaviours.

[26][27][28][29][30] Human chitinases may explain the link between some of the most common allergies (dust mites, mold spores—both of which contain chitin) and worm (helminth) infections, as part of one version of the hygiene hypothesis[31][32][33] (worms have chitinous mouthparts to hold the intestinal wall).

[35] The regulation of an endochitinase in Trichoderma atroviride is dependent on a N-acetylglucosaminidase, and the data indicates a feedback-loop where the break down of chitin produces N-acetylglucosamine, which would be possibly taken up and triggers up-regulation of the chitinbiosidases.

Phaseolus vulgaris,[40] bananas, chestnuts, kiwifruit, avocados, papaya, and tomatoes, for example, all contain significant levels of chitinase, as defense against fungal and invertebrate attack.

Some parts of chitinase molecules, almost identical in structure to hevein or other proteins in rubber latex due to their similar function in plant defense, may trigger an allergic cross-reaction known as latex-fruit syndrome.

[40] Possible future applications of chitinases are as food additives to increase shelf life, therapeutic agent for asthma and chronic rhinosinusitis, as an anti-fungal remedy, an anti-tumor drug and as a general ingredient to be used in protein engineering.