In vitro metabolic engineering of hydrogen production at theoretical yield from sucrose.

Hydrogen is one of the most important industrial chemicals and will be arguably the best fuel in the future. Hydrogen production from less costly renewable sugars can provide affordable hydrogen, decrease reliance on fossil fuels, and achieve nearly zero net greenhouse gas emissions, but current chemical and biological means suffer from low hydrogen yields and/or severe reaction conditions. An in vitro synthetic enzymatic pathway comprised of 15 enzymes was designed to split water powered by sucrose to hydrogen. Hydrogen and carbon dioxide were spontaneously generated from sucrose or glucose and water mediated by enzyme cocktails containing up to 15 enzymes under mild reaction conditions (i.e. 37°C and atm). In a batch reaction, the hydrogen yield was 23.2mol of dihydrogen per mole of sucrose, i.e., 96.7% of the theoretical yield (i.e., 12 dihydrogen per hexose). In a fed-batch reaction, increasing substrate concentration led to 3.3-fold enhancement in reaction rate to 9.74mmol of H2/L/h. These proof-of-concept results suggest that catabolic water splitting powered by sugars catalyzed by enzyme cocktails could be an appealing green hydrogen production approach.