Figure 2.

Chitinase activity. Arabidopsis thaliana chitinases were incubated with N‐acetyl‐d‐glucosamine (GlcNAc) oligomers with degree of polymerization 6 (dp6). Reactions consisted of 1 mm hexa‐N‐acetylchitohexaose (dp6) (Seikagaku, Tokyo, Japan) in sodium acetate buffer (10 mm, pH 5.2). Chitinase (0.01 mg protein/mL) was added and reactions were stopped by adding an equal volume of matrix (saturated 2,5‐dihydroxybenzoic acid in acetonitrile). Conversion of dp6 to a mixture of dp5, dp4, dp3 and dp2 was visualized by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) on a Bruker Daltonic OmniFlex instrument (Billerica, MA, USA).