NADH:ubiquinone reductase (non-electrogenic)

NADH:ubiquinone reductase (non-electrogenic)

Crystal structure of the hydrophilic domain of respiratory complex I from Thermus thermophilus

NADH:ubiquinone reductase (non-electrogenic), also known as complex I, is a crucial enzyme in the electron transport chain of mitochondria and some bacteria. It catalyzes the transfer of electrons from NADH to ubiquinone, a key step in cellular respiration. Unlike its electrogenic counterpart, this enzyme does not contribute to the generation of a proton gradient across the membrane.

Structure

The enzyme is a large, multi-subunit complex that is embedded in the inner mitochondrial membrane. It consists of a hydrophilic domain and a membrane domain. The hydrophilic domain contains the flavin mononucleotide (FMN) and several iron-sulfur clusters that facilitate electron transfer. The membrane domain is involved in the binding and reduction of ubiquinone.

Function

NADH:ubiquinone reductase (non-electrogenic) plays a pivotal role in the oxidative phosphorylation pathway. It initiates the electron transport chain by oxidizing NADH, which is produced in the citric acid cycle, and transferring the electrons to ubiquinone. This process is essential for the production of ATP, the energy currency of the cell.

Mechanism

The enzyme operates through a series of redox reactions. Electrons from NADH are transferred to FMN, then through a series of iron-sulfur clusters, and finally to ubiquinone, reducing it to ubiquinol. This electron transfer is coupled with conformational changes in the enzyme, although in the non-electrogenic form, these changes do not result in proton translocation across the membrane.

Biological Significance

The activity of NADH:ubiquinone reductase is vital for maintaining the redox balance within the cell and for the efficient production of ATP. It is also involved in the regulation of reactive oxygen species (ROS) production, which can have significant implications for cellular aging and disease processes.

Related pages

• Electron transport chain
• Oxidative phosphorylation
• Mitochondrion
• NADH
• Ubiquinone