Pyridoxamine phosphate

Pyridoxamine phosphate usually denotes pyridoxamine 5'-phosphate, the phosphate ester of the position-5 hydroxymethyl group of pyridoxamine. Its neutral-form molecular formula is ${\mathrm{C}}_8{\mathrm{H}}_{13}{\mathrm{N}}_2{\mathrm{O}}_5\mathrm{P}$. It is an active Vitamin B6 coenzyme form, chemically distinct from both free pyridoxamine and pyridoxal phosphate.^[ref][ref]

A concrete reaction distinguishes the two phosphorylated forms. Pyridoxal 5'-phosphate synthase can oxidatively convert pyridoxamine phosphate into pyridoxal phosphate, producing Ammonia and hydrogen peroxide while consuming water and oxygen.^[ref] The transformation changes the aminomethyl group into an aldehyde group while retaining the phosphate ester.

For an ideal $1\mu \mathrm{mol}$ conversion by this reaction, one micromole each of Ammonia and hydrogen peroxide is produced. A peroxide assay can consequently report a coupled reaction signal, but identifying the B6 product remains a separate analytical question. A peroxide-producing impurity could mimic that signal without making the intended coenzyme.