Two isozymes of 6-phosphoglucose isomerase (phosphoglucose isomerase A & phosphoglucose isomerase B), isolated from Bacillus stearothermophilus, have been overexpressed in Escherichia coli strain DF2145 and purified to homogeneity, Crystals of both isozymes have been obtained by the vapor diffusion method. The crystals of phosphoglucose isomerase A have unit cell dimensions a = b = 132.0 Angstrom, c = 183.6 Angstrom, and diffract to about 2.8 Angstrom resolution. An analysis of the reflection data indicates that the crystal system is hexagonal, space group P6(1)22 or P6(5)22, The crystals of phosphoglucose isomerase B complexed with 6-phosphogluconate belong to the orthorhombic space group I222 (or I2(1)2(1)2(1)), With cell dimensions a = 75.1 Angstrom, b = 95.7 Angstrom, c = 171.5 Angstrom, and diffract to a resolution of 2.3 Angstrom, These crystals promise to yield more detail for the substrate recognition and higher resolution structures of 6-phosphoglucose isomerase. (C) 1997 Academic Press.