Two different crystal forms of pig pancrleatic a-amylase isoenzyme I1 (PPAII), free and complexed to a carbohydrate inhibitor (acarbose), have been compared together and to previously reported structures of PPAI. A crystal form obtained at 4"C, containing nearly 72% solvent, made it possible to obtain a new complex with acarbose, different from a previous one obtained at 20°C [Qian, M., Buisson, G., DuCe, E., Haser, H. & Payan, F. (1994) Biocrbemistry 33, 6284-62941. In the present form, six contiguous subsites of the enzyme active site are occupied by the carbohydrate ligand; the structural data indicate that the binding site is capable of holding more than the five glucose units of the scheme proposed through kinetic studies. A monosaccharide ring bridging two protein molecules related by the crystal packing is located on the surface, at a distaince of 2.0 nm from the reducing end of the inhibitor ligand; the symmetry-related glucose ring in the crystal lattice is found 1.5 nm away from the non-reducing end of the inhibitor ligand.

No abstract

No abstract

No abstract