This is due to the presence of a dinuclear iron centre,[3] to which a tyrosine residue is connected via a charge transfer.
Upon treatment with mild reductants, PAPs are converted to their enzymatically active, pink form.
Treatment with strong reducing agents dissociates the metallic ions, and renders the enzyme colourless and inactive.
[7] However sequence analysis reveals that there is minimal homology between plant and mammal PAPs (<20%), except for the metal-ligating amino acid residues which are identical.
There is, however, a consensus in the literature that purple acid phosphatase (PAP) relates to those found in non-mammalian species and tartrate resistant acid phosphatase (TRAP) to those found in mammalian species.