alpha-Mannosidase from Phaseolus vulgaris. Composition and structural properties.

Both alpha-mannosidases I and II from Phaseolus vulgaris have molecular weights about 210000-220000 and contain approximately 2 mol zinc/mol protein. alpha-Mannosidase I seems to consist of more glutamic acid than alpha-mannosidase II, while the latter is richer in serine. They are glycoproteins: alpha-mannosidase I contains 8.3% carbohydrate by weight while alpha-mannosidase II contains 16.5%. This enzyme form shows a greater thermal stability than alpha-mannosidase I. The structure of alpha-mannosidase has been investigated by equilibrium sedimentation analysis in guanidine hydrochloride, electrophoresis in dodecylsulphate, and alkaline electrophoresis after exposure to high pH. The protein appears to be composed of two non-covalently bound subunits of molecular weights about 110000. Electron micrographs revealed images of molecules that consisted of two rod-shaped monomers of roughly square cross-sections 4.2 X 4.2 nm. Each rod was about 7.4 nm long. The monomers seemed parallell along the long axis.