In an effort that should help those working towards ‘solar H2-farms’ in which microorganisms produce bio hydrogen fuel from sunlight and water, scientists from Oxford University and universities in Germany have discovered how oxygen stops green algae from producing hydrogen.

Oxygen and Carbon Dioxide At an Enzyme. Click image for a larger view.

Oxygen and Carbon Dioxide At an Enzyme. Click image for a larger view.

The international European team have reported the results two papers, one in the journal JACS and one in PNAS, published last week.

Scientists have for years been interested in how science could, potentially, produce hydrogen from just sunlight and water to power vehicles and other devices. One option is the closely studied method to use photosynthetic microorganisms that are able to produce hydrogen in the process of making starch. Green algae are one of the microorganisms that many have suggested could be turned into living hydrogen factories.

Professor Fraser Armstrong from Oxford University’s Department of Chemistry, an author of both papers said, “The hydrogen-producing enzyme found in green algae, known as an iron-iron hydrogenase, has evolved a structure that makes it particularly susceptible to attacking oxygen molecules.  Because oxygen is a major by-product of the hydrogen-making photosynthetic process in such organisms, the build-up of oxygen, which rapidly attacks the active site of the enzyme, quickly brings the hydrogen-making process to an irreversible halt. Our work has revealed the mechanism of this process.”

In the JACS abstract the authors point out a major obstacle for future bio hydrogen production is the oxygen sensitivity of [FeFe]-hydrogenases, the highly active catalysts produced by bacteria and green algae. The study work is then answered in the PNAS study saying, carbon monoxide, a competitive inhibitor of CrHydA1 which binds to an Fe atom of the 2FeH domain and is otherwise not known to attack FeS clusters in proteins, reacts nearly two orders of magnitude faster than oxygen and protects the enzyme against oxygen damage. These results therefore show that destruction of the [4Fe-4S] cluster is initiated by binding and reduction of oxygen at the di-iron domain—a key step that is blocked by carbon monoxide.

The team used electrochemical kinetic methods to determine the order of events in which the oxygen attacks the active site of an iron-iron hydrogenase found in the green algae Chlamydomonas reinhardtii. They combined their observations with data obtained from X-ray absorption spectroscopy. By measuring ripples in the photoelectron energy spectrum of the enzyme under X-ray bombardment they were able to deduce the nature of the damage caused to the active site following attack by oxygen.

Yet while the research reported in PNAS shows just how destructive oxygen is to the enzyme powering green algae’s hydrogen-making process, the team’s research reported in JACS shows that similar hydrogenases produced by other microorganisms may possess greater tolerance to oxygen, sufficient perhaps to survive in the presence of oxygen released during photosynthetic hydrogen production.

Confused?  The point the researchers could make to the layperson is that different organisms have different responses to the molecules in their close environment and that oxygen isn’t very helpful to destructive while carbon monoxide can be of marginal value to improving results by two orders of magnitude.  Keep in mind, all of this is happening to the hydrogenase enzyme operating inside the organism.

The news is in Professor Armstrong’s remark, “It shows that whilst we may have found a major obstacle along one route to the biological production of hydrogen, this knowledge could help us to identify new routes where nature could suggest an answer to the problem of oxygen’s destructive effect on hydrogen-producing enzymes.”

The layperson’s puzzle is that usually carbon monoxide is a toxin or poison. The research has pointed out, that just as the carbon monoxide taken in a breath displaces oxygen at the red blood cell level it can also displace oxygen in the algae where the oxygen inhibits the production of hydrogen.

But its not resolved that an algae can yet absorb a bit of CO to keep its enzymes working.  Yet now it’s clear that that path of designing algae genetics such that the organism’s close environment with some CO could have a major payoff.

It’s not often that a biological path is seen so simply.  Although the researchers aren’t saying so, the bug designers have a hard clue on what attributes the new bugs will need to get that hydrogen output up.

On the other hand, this is very early research and getting from the “why” exposed by the research to the designer organism getting the job done is a long way and not a sure thing.

But getting the needed hydrogen, and the fuels of the future are going to need huge amounts of it, is a major job that deserves lots of attention, skill, innovation, and funding.

This research is a major success.


2 Comments so far

  1. On the Path to Free Hydrogen from Biology | New Energy and Fuel : Science and Technology News on October 13, 2009 5:57 AM

    […] On the Path to Free Hydrogen from Biology | New Energy and Fuel […]

  2. Jason Ford on October 21, 2009 3:54 AM

    Hey..Great work..thanks for mentioning the important facts and data..I do believe that hydrogen is the future of fuel..i really like the information thanks! and keep posting.

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