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Biosynthesis of the unusual organometallic H-cluster at the active site of the FeFe-hydrogenase requires three accessory proteins, two of which are radical AdoMet enzymes (HydE, HydG) and one of which is a GTPase (HydF). We demonstrate here that HydG catalyzes the synthesis of CO using tyrosine as a substrate. CO production was detected by using deoxyhemoglobin as a reporter and monitoring the appearance of the characteristic visible spectroscopic features of carboxyhemoglobin. Assays utilizing (13)C-tyrosine were analyzed by FTIR to confirm the production of HbCO and to demonstrate that the CO product was synthesized from tyrosine. CO ligation is a common feature at the active sites of the FeFe, NiFe, and Fe-only hydrogenases; however, this is the first report of the enzymatic synthesis of CO in hydrogenase maturation.
Shepard et al. (Mon,) studied this question.