Investigations of the catalytic and structural transitions of jack bean alpha-mannosidase (Jb alpha-man) are described in the present paper. The enzyme was maximally stable at pH 5.0; however, when incubated in the pH range of 11.0-12.0, showed 1.3 times higher activity and also stability for longer time. The free amino group at or near the active site was probably involved in the stability and activation mechanism. The active site is constituted by the association of two unidentical subunits connected by disulfide linkages. The metalloenzyme has Zn(2+) ions tightly bound and chelation reduces the thermal stability of the protein. Energetics of catalysis and thermodynamics of inhibition of the enzyme were also carried out. (C) 2011 Elsevier B.V. All rights reserved.

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