The structure of alanine racemase from Bacillus stearothermophilus (Geobacillus stearothermophilus) was determined by X-ray crystallography to a resolution of 1.9 A. The alanine racemase monomer is composed of two domains, an eight-stranded alpha/beta barrel at the N terminus, and a C-terminal domain essentially composed of beta-strand. The N-terminal domain is also found in the PROSC (proline synthetase co-transcribed bacterial homolog) family of proteins, which are not known to have alanine racemase activity. The pyridoxal 5'-phosphate (PLP) cofactor lies in and above the mouth of the alpha/beta barrel and is covalently linked via an aldimine linkage to a lysine residue, which is at the C terminus of the first beta-strand of the alpha/beta barrel.
^Shaw JP, Petsko GA, Ringe D (February 1997). "Determination of the structure of alanine racemase from Bacillus stearothermophilus at 1.9-A resolution". Biochemistry36 (6): 1329–42. doi:10.1021/bi961856c. PMID9063881.