Embargoed for 5 P.M., EST
NSF PR 98-80 - December 3, 1998
This material is available primarily for archival
purposes. Telephone numbers or other contact information
may be out of date; please see current contact information
at media
contacts.
Scientists Describe Structure Of An Enzyme That Uses
Iron To Make Hydrogen
The workings of an iron-laden bacterial enzyme could
one day provide researchers with an inexpensive and
stable catalyst to create hydrogen, according to scientists
at Utah State University.
With funding from the National Science Foundation
(NSF), biochemists John Peters and Lance Seefeldt
have made a detailed description of the structure
of an enzyme known as CpI, found in the soil microorganism
Clostridium pasteurianum. The results of their research
on the structure and function of CpI are published
in the December 4 issue of the journal Science.
CpI is a hydrogenase, a type of enzyme used by microorganisms
to make molecular hydrogen (H2), or through reversing
the reaction, break down H2 into protons and electrons.
Peters and Seefeldt's study suggests a mechanism by
which CpI uses atoms of iron as a means to catalyze
the production of H2.
"The iron-only hydrogenase is basically a means to
get rid of unwanted electrons," said Kamal Shukla,
NSF program manager. "Clostridium pasteurianum uses
CpI to convert protons and electrons into (H2), a
waste product."
What is a waste product to some organisms might be
an incredibly useful product for others. According
to Peters, a better understanding of this enzymatic
process interests not only biologists and biochemists,
but also researchers of alternative energy sources.
"Hydrogen is often mentioned as a future fuel source
because it is a renewable and clean-burning energy
carrier," said Peters. "The biological production
of hydrogen, then, represents a tremendous reserve
of energy that we may tap through our understanding
of the mechanisms that have evolved in nature."
Attaining the three-dimensional structure of enzymes
like CpI may be the first step in tapping into that
resource. Peters and Seefeldt depict CpI as a collection
of 20 iron atoms arranged in clusters around a mushroom
shaped framework. Electrons move in through the `stem'
of the mushroom in a series of reactions between the
iron clusters that pass electrons, like a molecular
bucket brigade, towards the `cap' of the mushroom.
The `cap' contains the active site of the enzyme,
where the final reaction takes place.
At the active site, more clusters of iron atoms introduce
electrons, two at a time, to two protons stripped
from a single molecule of water. As newly formed molecules
of hydrogen leave the enzyme, they make room for more
electrons and protons to take their spot, providing
the energy for the next reaction to take place.
"Hopefully, through knowing the structure of the iron-only
hydrogenase, protein engineers can work on methods
to increase the stability of the enzyme," said Peters.
"Once in industrial use, such an efficient source
of clean energy is likely to be both economically
and environmentally significant."
|