Enzymes may turn paper, grass into fuel.

Imagine generating enough fuel from grass clippings, old newspapers, corn syrup, and cheese whey to run a car, light up a house, or heat a city. That flight of fancy remains science fiction, but investigators may have taken a small step toward realizing it with their recent development of an enzymatic method of transforming such renewable resources into hydrogen gas.

The prospect of using hydrogen as an environmentally friendly, or clean, fuel has long tantalized energy researchers. Unlike fossil fuels, whose combustion creates many pollutants, hydrogen generates little besides water when it burns. Moreover, in devices called fuel cells, hydrogen reacts efficiently with oxygen to produce electricity.

Hydrogen power has not yet been embraced by the world, in part because of an ironic scarcity of the ubiquitous element: Hydrogen is almost always bound up in chemical compounds. Current methods of hydrogen production include liberating it from water with the use of electricity, a technique called electrolysis, or breaking methane and other fossil fuels into their essential components, which include hydrogen.

Yet electrolysis is not cost-effective. Moreover, using nonrenewable fossil fuels to make hydrogen is not a favored long-term option, partly because that strategy generates waste gases such as carbon dioxide and carbon monoxide. Enzymes stolen from bacteria may now offer another hydrogen production option, contend Jonathan Woodward of Oak Ridge (Tenn.) National Laboratory and his colleagues. In the July Nature Biotechnology, they provide the first demonstration that a simple two-enzyme system can generate hydrogen gas from glucose.

"It's a long way from anything commercially viable, but I think it's a nice demonstration that such things are possible," comments Richard Cammack, who studies hydrogen production methods at King's College in London.

The new process first combines glucose with a bacterial enzyme called glucose dehydrogenase. In the presence of a compound known as NADP, this enzyme transforms a glucose molecule into gluconic acid and attaches a freed hydrogen atom to NADP, forming NADPH. Another enzyme, a hydrogenase isolated from bacteria found in a deep-sea hydrothermal vent, then releases the hydrogen from NADPH, generating hydrogen gas and enabling NADP to repeat the cycle. Glucose would come from renewable resources such as cellulose, lactose, and starch, say the researchers. Wood pulp, grass clippings, and newspapers are excellent sources of cellulose that simply go to waste, Woodward points out. In Wisconsin, whey created in the process of making cheese offers a significant source of lactose, he adds.

Woodward's group has calculated that the cellulose in the waste newspaper generated each year in the United States could theoretically provide enough hydrogen to meet the energy demands of 37 cities the size of Oak Ridge, which has a population of around 27,000.

"We need to optimize conditions for hydrogen production, something I don't think we've achieved yet. Right now, the majority of material generated is not hydrogen, it's gluconic acid," says Woodward. While that product may also be mined for additional hydrogen atoms, gluconic acid itself is a valuable chemical compound currently used by a number of industries.