pyridoxine 5′-phosphate oxidase has been highly conserved over time, as there are many similarities between the enzyme as it is found in humans and "escherichia coli". although there is only 39% retention of amino acid sequence from the "e. coli" version of the enzyme to the human version, the sequences for the fmn binding site and the substrate active sites are among the very highly conserved portion. one of the key differences is that the human pyridoxine 5′-phosphate oxidase has a higher specificity for the pyridoxamine 5′-phosphate substrate, whereas the pyridoxine 5′-phosphate oxidase in "e. coli" has a higher specificity pyridoxal 5′-phosphate substrate.