FDHH

FdhH, or formate dehydrogenase H, is a molybdenum-containing enzyme found in several anaerobic bacteria, most notably Escherichia coli. It functions as a component of the formate hydrogenlyase (FHL) complex, which couples the oxidation of formate to the production of molecular hydrogen. In organisms that possess it, FdhH transfers electrons released from formate oxidation to membrane-associated hydrogenases, enabling hydrogen production and carbon dioxide release under anaerobic conditions.

Biochemical features of FdhH place it among formate dehydrogenases that contain a molybdenum cofactor and iron-sulfur centers. The catalytic activity involves a molybdenum-containing active site that accepts formate and initiates electron transfer within the FHL assembly. Through interactions with hydrogenase components of the complex, electrons are conveyed toward protons, contributing to energy metabolism or hydrogen formation depending on cellular conditions.

Genetic and regulatory context varies among species but typically includes operons encoding multiple FHL components, among them FdhH. Expression of these operons is commonly upregulated during anaerobic growth and in the presence of formate, reflecting a role in facilitating anaerobic energy production. Maturation and assembly factors ensure proper incorporation of cofactors and the integration of FdhH into the FHL complex.

Localization and organization describe FdhH as part of the FHL complex associated with the cytoplasmic membrane in bacteria. The assembly brings together formate dehydrogenase activity with hydrogenase components, creating a coordinated pathway for formate oxidation and subsequent hydrogen production or electron transfer to the respiratory chain.

Research and applications focus on understanding anaerobic energy metabolism and microbial hydrogen production, with potential implications for bioenergy and biotechnological processes leveraging FHL systems.