hydrogenasesenzymes

Hydrogenases are enzymes that catalyze the reversible interconversion of molecular hydrogen (H2) and protons with electrons, enabling hydrogen metabolism in cells. They are found in a wide range of organisms, including bacteria, archaea, and some unicellular eukaryotes, and play important roles in energy conservation, redox balance, and hydrogen cycling in ecosystems.

Hydrogenases are mainly classified by their active site metal composition into three major families: [NiFe]-hydrogenases, [FeFe]-hydrogenases, and [Fe]-hydrogenases. The active centers contain metal ions coordinated by ligands and are connected to electron transfer chains via iron-sulfur clusters. The general reaction is H2 ↔ 2H+ + 2e−, with electrons taken up by cellular carriers such as ferredoxin, NAD(P)+, or quinones, depending on the enzyme type and organism. This allows hydrogenases to function in hydrogen uptake during respiration or hydrogen production during fermentation and other anaerobic processes.

Subtypes include uptake hydrogenases, which oxidize H2 to feed electrons into the respiratory chain, and bidirectional hydrogenases, which can either consume or produce H2 to balance cellular redox. Many enzymes are part of larger energy-conserving systems and are associated with membrane components or cytosolic electron carriers. A common feature is sensitivity to oxygen in many [NiFe]- and [FeFe]-hydrogenases, although several oxygen-tolerant variants have been identified under specific conditions.

Applications and relevance include potential use in biohydrogen production, biocatalysis, and biosensing. Research continues to address challenges such as oxygen sensitivity, stability, and integration into renewable-energy systems, while highlighting hydrogenases’ role in microbial metabolism and the global hydrogen cycle.