Structural bases for the catalytic mechanism of Ni-containing carbon monoxide dehydrogenases.

Significant progress has been made recently in our understanding of the structure/function relationships of the catalytic C-cluster of carbon monoxide dehydrogenases. Several structures of this enzyme have been reported, some of them at very high resolution. One recurrent problem, however, is the high degree of heterogeneity within each structure, as well as between the different X-ray models. Here, we have tried to relate the structural data with the wealth of spectroscopic and biochemical information gathered over many years. As a result, we propose a catalytic cycle that is consistent with both observations and stereochemistry. We also give alternatives to one of the most difficult aspects of the cycle, namely, the location of the two electrons in the most reduced state of the C-cluster.