The leaves of Boscia senegalensis are traditionally used in West Africa in cereal protection against pathogens, pharmacologic applications, and food processing. Activities of alpha -amylase, beta -amylase, exo-(1 -->3, 1 -->4)-beta -D-glucanase, and endo-(1 -->3)-beta -D-glucanase were detected in these leaves. The endo-(1 -->3)-beta -D-glucanase (EC 3.2.1.39) was purified 203-fold with 57% yield. The purified enzyme is a nonglycosylated monomeric protein with a molecular mass of 36 kDa and pI greater than or equal to 10.3. Its optimal activity occurred at pH 4.5 and 50 degreesC. Kinetic analysis gave V-max, k(cat), and K-m values of 659 U/mg, 395 s(-1), and 0.42 mg/mL, respectively, for laminarin as substrate. The use of matrix-assisted laser desorption ionization time-of-flight mass spectrometry and high-performance liquid chromatography revealed that the enzyme hydrolyzes not only soluble but also insoluble (1 -->3)-beta -glucan chains in an endo fashion. This property is unusual for endo-acting (1 -->3)-beta -D-glucanase from plants. The involvement of the enzyme in plant defense against pathogenic microorganisms such as fungi is discussed.