The chemical reactions catalyzed by thyroid peroxidase occur on the outer apical membrane surface and are mediated by hydrogen peroxide.

Ascidians (tunicates or sea squirts) and amphioxus, which are close invertebrate relatives of vertebrates, have a primitive homolog of the thyroid known as the endostyle.

Coupling of DIT to MIT in the opposite order yields a substance, r-T3, which is biologically inactive.

[8] In laboratory rats with insufficient iodine intake, genistein has demonstrated inhibition of TPO.

[12] TPO's ability to non-selectively couple tyrosine residues together has been used to modify protein tags.