Hydrogen sulfide bypasses the rate-limiting oxygen activation of heme oxygenase.

Discovery of unidentified protein functions is of biological importance because it often provides new paradigms for many research areas. Mammalian heme oxygenase (HO) enzyme catalyzes the O-dependent degradation of heme into carbon monoxide (CO), iron, and biliverdin through numerous reaction intermediates. Here, we report that HS, a gaseous signaling molecule, is part of a novel reaction pathway that drastically alters HO's products, reaction mechanism, and catalytic properties.