Figure 1.

Schematic representation of the two disparate mechanisms used to explain IspH catalysis. Both the Birch reduction and organometallic mechanisms attempt to explain how IspH catalyzes the 2e^–/2H⁺ reductive dehydroxylation of HMBPP (3) to afford IPP (1) and DMAPP (2) in an approximate 5:1 ratio.