In the coming decade, our planet is going to face several environmental and energy related problems which directly relate to the biological fixation of carbon dioxide CO2 into organic carbon which forms a major part of the CO2 and the carbon biogeochemical cycle. Anaerobic microbes can fix CO2 to CO and use CO to generate acetyl CoA. They are also capable of CO detoxification by reversibly oxidizing CO into CO2. The key enzymatic machinery for such processes is the monoxide dehydrogenase (CODH) and acetyl- coenzyme A synthase (ACS) enzymatic complex. This enzymatic complex is the subject of an intense research activity for its potential industrial application. Key to its function is the diffusion of substrates (including inhibitors such as O2) in the protein matrix. The purpose of the proposal is to computationally characterize the diffusion channels and escape routes for CO2 and CO in a variety of CODH/ACS complexes. At the same time, we aim at designing mutants that prevent O2 diffusion and, consequently, enzymatic inhibition.