Pyrocatechol its sulfonic acid is often present in the urine of many mammals. Small amounts of catechol occur naturally in fruits and vegetables along with the enzyme polyphenol oxidase. Upon mixing the enzyme with the substrate and exposure to oxygen (as when a potato or apple is cut) the colorless catechol oxidizes to reddish-brown benzoquinone derivatives.

RGD peptide (GRGDNP) (TFA) promote apoptosis through activation of conformation changes that enhance pro-caspase-3 activation and autoprocessing.

The branches of Rhamnus cathartica.