pyridoxine 5′-phosphate oxidase is a homodimer, or a molecule consisting of two identical polypeptide subunits. it is hypothesized that the two monomers are held together by disulfide bonds. there are also salt-bridge interactions between the two monomers. each subunit tightly binds one molecule of pyridoxal 5′-phosphate tightly on each subunit. both alpha-helices and beta-sheets are present in the protein motif, which is best described as a split-barrel structure. this structure is due, in part, to the disulfide bonds present in the secondary protein structure of this enzyme. multiple thiol groups (–sh) indicate the presence of disulfide bonds in the structure of the molecule. this enzyme requires the presence of a cofactor, fmn (flavin mononucleotide).