Biochemistry of Methyl-Coenzyme M Reductase: The Nickel Metalloenzyme that Catalyzes the Final Step in Synthesis and the First Step in Anaerobic Oxidation of the Greenhouse Gas Methane - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 125

methanogenesis because it involves a pathway that involves an MCR-like Ni
protein [ 17 , 21 ] and the other enzymatic steps involved in methanogenesis.
The first reaction in AOM is the direct reverse of reaction (1) and, given that
the reverse reaction is highly endothermic( G 0 , mol), coupling to sulfate

or nitrate reduction is required to make the process thermodynamically feasible.

Δ ¼ þ 30 kJ =

1.3 Ramifications of Methanogenesis in Energy
and the Environment

Methane, the major component of natural gas, has been in use in human civilization
since ancient times (6000 to 2000 bce) where it appears to have provided fuel for
the “eternal fires” of the ancient Persians. Methane from animal waste was used for
heating in Assyria. By 200 bce, the Chinese were drilling wells with bamboo poles
to depths of 150 meters and, in the 12th century, Marco Polo mentioned in writings
of his travels the use of covered sewage tanks to generate power in China.
Today, methane accounts for 22% of U.S. energy consumption [ 22 , 23 ], with
slightly more than half of homes using natural gas as their heating fuel. It is the
simplest organic compound and has the highest energy content of any carbon-based
fuel. Widely mined and used as a fuel for heating and cooking, methane also is used
by the chemical industry to produce synthesis gas, to generate electricity, and to
serve as a vehicle fuel in the form of compressed or liquid natural gas. Methane is
considered a clean fuel because it emits less sulfur, carbon, and nitrogen than coal
or oil, and leaves little ash.
Methane utilization also has environmental ramifications because it is a potent
greenhouse gas whose levels have doubled over the past two centuries [ 24 ].
This rapid increase in concentration has created a mismatch between the sources
and sinks of methane, causing an increasing amount of this gas to escape into
the atmosphere. This is a source of concern because methane is 21 times more
effective at trapping heat in the atmosphere than the major greenhouse gas, carbon
dioxide [ 25 ].
It is hoped that obtaining a better understanding of the chemistry and biology
related to methane metabolism will lead to biotechnological advances for decreased
reliance on fossil fuels and remediation of greenhouse gas-caused climate change.

1.4 Discoveries Underpinning Recent Studies
of Methyl-Coenzyme M Reductase

In what is generally accepted as the earliest scientific studies of methanogenesis,
the Italian physicist Alessandro Volta and Father Carlo Campi performed many
experiments around the turn of the 19th century on the “combustible air” from
marshy soil [ 26 ]. Volta made a combustion chamber, a sort-of calorimeter,