Life as aerobes: are there simple rules for activation of dioxygen
by enzymes?
J Biol Inorg Chem, 6 (1):
1--13 (January 2001)Abstract
Numerous biological systems involve reaction with dioxygen in the
absence of readily accessible spectroscopic signals. We have begun
to develop a set of "generic" strategies that will allow us to probe
the mechanisms of dioxygen activation. In particular, we wish to
understand the nature of the dioxygen binding step, the degree to
which electron transfer to dioxygen is rate limiting, whether reactive
species accumulate during turnover and, finally, whether proton
and electron transfer to dioxygen occur as coupled processes. Our
strategy will be introduced for an enzyme system that uses only
an organic cofactor in dioxygen activation (glucose oxidase). Two
key features emerge from studies of glucose oxidase: (1) that formation
of the superoxide anion is a major rate-limiting step and (2) that
electrostatic stabilization of the superoxide anion plays a key
role in catalysis. Similar themes emerge when our protocols are
applied to enzymes containing both an active site metal center and
an organic cofactor. Finally, enzymes that rely solely on metal
centers for substrate functionalization will be discussed. In no
instance, thus far, has evidence been found for a direct coupling
of proton to electron transfer in the reductive activation of dioxygen.