Approaches to developing biological H2-photoproducing organisms and processes

The development of efficient biological systems for the direct photoproduction of H-2 gas from water faces several challenges, the more serious of which is the sensitivity of the H-2-evolving enzymes (hydrogenases) to 02, an obligatory by-product of photosynthesis. This high sensitivity is common to both FeFe and NiFe hydrogenases, and is caused by O-2 binding to their respective metallocatalytic sites. This overview describes approaches to (i) molecular engineering of algal FeFe-hydrogenase to prevent 02 access to its catalytic site; (ii) transform a cyanobacterium with an O-2-tolerant bacterial NiFe hydrogenase or (c) partially inactivate algal O-2-evolution activity to create physiologically anaerobiosis and induce hydrogenase expression.