DIRECT ELECTROCHEMISTRY OF MEGASPHAERA-ELSDENII IRON HYDROGENASE - DEFINITION OF THE ENZYMES CATALYTIC OPERATING POTENTIAL AND QUANTITATIONOF THE CATALYTIC BEHAVIOR OVER A CONTINUOUS POTENTIAL RANGE
Jn. Butt et al., DIRECT ELECTROCHEMISTRY OF MEGASPHAERA-ELSDENII IRON HYDROGENASE - DEFINITION OF THE ENZYMES CATALYTIC OPERATING POTENTIAL AND QUANTITATIONOF THE CATALYTIC BEHAVIOR OVER A CONTINUOUS POTENTIAL RANGE, European journal of biochemistry, 245(1), 1997, pp. 116-122
The Fe-hydrogenase from Megasphaera elsdenii undergoes direct electron
exchange with glassy carbon electrodes. Cyclic voltammetry defines th
e catalytic performance of the enzyme over a continuous but precisely
defined range of potentials. In the presence of H-2 and protons the bi
as of the enzyme towards H-2 production is readily visualised. Variati
on of the response with pH indicates that protein ionisations with pK
of approximately 6.7 and 8.3 regulate the catalytic activity. Possible
origins for these observations in the chemistry of the H-2-activating
site are discussed. The mid-wave potential of the catalytic response,
E(mid), is defined as the catalytic operating potential of the enzyme
. Under an atmosphere of hydrogen E(mid) = -421+/-10 mV, pH 7 with a v
ariation of -21+/-4 mV pH(-1), 22 degrees C. Deviation of E(mid) from
the thermodynamic potential of the hydrogen/proton couple reflects the
enzyme's influence over the catalysed reaction. E(mid) is the reducti
on potential of the H-2-activating centre (H-cluster) in the absence o
f kinetic bottle-necks at other steps in the reaction mechanism.