Abstract
One useful synthetic reaction missing from nature's toolbox is the direct hydrogenation of substrates using hydrogen. To create an enzyme that can directly reduce organic substrates with hydrogen, researchers have combined metal hydrogenation catalysts with proteins. A direct hydrogenation of olefins catalyzed by rhodium(I) bound to carbonic anhydrase (CA) was reported by Kazlauskas and the colleagues recently. They minimized nonspecific binding of rhodium by replacing histidine residues on the protein surface using site-directed mutagenesis or by chemically modifying the histidine residues. Hydrogenation catalyzed by their Rh-bound CA is slightly slower than for uncomplexed rhodium(I), but the protein environment induces stereoselectivity favoring cis-over trans-stilbene by about 20:1. This enzyme is the first cofactor-independent reductase that reduces organic molecules using hydrogen.
