Metabolism in marine flatfish-V. Chitinolytic activities in Dover sole, Solea solea (L.)

1. 1. Chitinolytic activity was studied in the digestive tract of Dover sole Solea solea (L.) using chitin based substrates and synthetic substrates. 2. 2. The initial hydrolysis of chitin appeared to be in the stomach at a pH of 2-3. This activity was detected using glycol chitosan, chitin azure and colloidal chitin as substrates, with minor activity towards 3,4-dinitrophenyl tetra N-acetyl ß-d-chitotetraoside in this pH region. 3. 3. This latter substrate was, however, readily hydrolysed at pH 5. At this pH homogenates of the digestive tract of Dover sole also showed activity towards the other substrates tested, with the exception of chitin azure and colloidal chitin. 4. 4. Chitin azure, colloidal chitin and glycol chitosan were hydrolysed at pH values of 8-9 (in addition to their hydrolysis at acid pH values) and it is likely that this alkaline chitinase was originating from intestinal bacteria. 5. 5. The hydrolysis of 3,4-dinitrophenyl tetra N-acetyl ß-d-chitotetraoside by intestinal extracts showed a similar profile to that obtained when a cell suspension of Micrococcus lysodeikticus was used as substrate, with an optimum value at pH 5.0-5.5. It is therefore probable that the hydrolysis of substrates at this pH was due to lysozyme. © 1988.