Final Stages in the Biosynthesis of the [FeFe]-Hydrogenase Active Site.

The paper aims to elucidate the final stages in the biosynthesis of the [2Fe] H active site of the [FeFe]-hydrogenases. The recently hypothesized intermediate [Fe 2 (SCH 2 NH 2 ) 2 (CN) 2 (CO) 4 ] 2- ([1] 2- ) was prepared by a multistep route from [Fe 2 (S 2 )(CN)(CO) 5 ] - . The following synthetic intermediates were characterized in order: [Fe 2 (SCH 2 NHFmoc) 2 (CNBEt 3 )(CO) 5 ] - , [Fe 2 (SCH 2 NHFmoc) 2 (CN)-(CO) 5 ] - , and [Fe 2 (SCH 2 NHFmoc) 2 (CN) 2 (CO) 4 ] 2- , where Fmoc is fluorenylmethoxycarbonyl). Derivatives of these anions include [K(18-crown-6)] + , PPh 4 + and PPN + salts as well as the 13 CD 2 -isotopologues. These Fe 2 species exist as a mixture of two isomers attributed to diequatorial (ee) and axial-equatorial (ae) stereochemistry at sulfur. In vitro experiments demonstrate that [1] 2- maturates HydA1 in the presence of HydF and a cocktail of reagents. HydA1 can also be maturated using a highly simplified cocktail, omitting HydF and other proteins. This result is consistent with HydA1 participating in the maturation process and refines the roles of HydF.