Protection of cyclooxygenase activity during heme-induced destabilization

Abstract

Sheep vesicular gland cyclooxygenase is destroyed spontaneously when incubated with only substoichiometric amounts of heme. Peroxides may participate in this destruction, since glutathione peroxidase, catalase, and phenol, a cosubstrate for prostaglandin hydroperoxidase, all protect the cyclooxygenase activity. Stoichiometric or greater levels of heme also tend to protect the enzyme from inactivation. Therefore, to achieve optimal recoveries of enzyme activity during purification and storage, the addition of prostaglandin hydroperoxidase cosubstrate, such as phenol, in combination with high levels of heme is recommended. The current understanding of destabilization and protection of cyclooxygenase now allows an interpretation of the previously unexplained phenomenon of slow phenol activation of cyclooxygenase acetone powder preparations. Phenol appears to protect enzyme activity during the slow equilibration of apoenzyme with endogenous heme to form the active holoenzyme. In the absence of phenol, the progressive rise in activity is not seen as the enzyme is vulnerable to heme-induced destruction.