Nearly all metabolic processes require protons—positively charged hydrogen atoms. Although these are abundant in the cellular fluid, the biocatalysts involved depend on mechanisms for efficiently capturing protons and transporting them to the site where catalysis occurs. Enzymes from microorganisms can produce hydrogen (H₂) by combining electrons with protons. These so-called hydrogenases are so efficient that one biocatalyst can capture nearly 10,000 protons per second.