Chemistry Reference
In-Depth Information
FIGURE 14.14
Human SOD1 showing the disulfide bond in blue in the
b
-strand which forms the bulk of the dimer interface (in blue) with the
Cu and Zn ions as blue and green spheres. In the right monomer, MBr mutations are shown as yellow spheres. (From
Hart, 2006
. Copyright
2006, with permission from Elsevier.)
Copper enzymes are involved in reactions with a large number of other, mostly inorganic, substrates. In
addition to its role in oxygen and superoxide activation described above, copper is also involved in enzymes which
activate methane, nitrite, and nitrous oxide.
There are vast reserves of methane gas in the world, which are currently underutilised as a feedstock for the
production of liquid fuels and chemicals because of the lack of economical and sustainable strategies for the selective
oxidation of methane to methanol. Current processes require high temperatures, are costly and inefficient, and
produce waste, yet throughout nature methanotrophic bacteria perform this reaction under ambient conditions using
methane monooxygenases (MMOs). We already encountered the soluble di-iron MMO in Chapter 13, expressed by
several strains of methanotroph under copper-limited conditions. All methanotrophs produce membrane-bound
particulate MMO (pMMO). Yet, in spite of 20 years of research and the availability of two crystal structures, the
metal composition and location of the pMMO metal active site were still not known until very recently. In 2010, the
structure of particulate methane monooxygenase from the methanotrophic bacteria M. capsulatus was determined at
a
3
b
3
g
3
polypeptide arrangement. Two metal centres,
modeled as mononuclear and dinuclear copper are located in the soluble part of each
b
-subunit, which resembles
