Transient oxidation as a mechanistic strategy in enzymatic catalysis

Enzymes that employ a transient oxidation mechanism catalyze transformations that are overall redox neutral, but involve intermediates that have a higher oxidation state than the substrates or products. An oxidation/reduction sequence may be used directly to promote isomerization reactions or indirectly to permit the formation of stabilized intermediates such as carbanions. This review will focus on three recent examples of nicotinamide-dependent enzymes that have been found to employ transient oxidation during catalysis: ADP-L-glycero-D-manno-heptose 6-epimerase, GDP-mannose 3,5-epimerase, and the 6-phosphoglucosidases from family 4. These enzymes are remarkable in their ability to catalyze either nonstereospecific hydride transfers or multiple chemical steps within a single active site.