Hydrogen Tunneling in a Prokaryotic Lipoxygenase

[Image: see text] A bacterial lipoxygenase (LOX) shows a deuterium kinetic isotope effect (KIE) that is similar in magnitude and temperature dependence to the very large KIE of eukaryotic LOXs. This occurs despite the evolutionary distance, an ∼25% smaller catalytic domain, and an increase in E(a) of ∼11 kcal/mol. Site-specific mutagenesis leads to a protein variant with an E(a) similar to that of the prototypic plant LOX, providing possible insight into the origin of evolutionary differences. These findings, which extend the phenomenon of hydrogen tunneling to a prokaryotic LOX, are discussed in the context of a role for protein size and/or flexibility in enzymatic hydrogen tunneling.