Succinate as Donor; Fumarate as Acceptor.

Area of Science:

• Biochemistry
• Molecular Biology
• Bioenergetics

Background:

• Succinate and fumarate are four-carbon dicarboxylates central to cellular respiration.
• Their interconversion via oxidoreduction is vital for both aerobic and anaerobic energy metabolism.

Purpose of the Study:

• To summarize the structure, function, and regulation of succinate:ubiquinone oxidoreductase (SQR) and fumarate:menaquinol oxidoreductase (QFR).
• To elucidate the mechanisms underlying succinate:fumarate interconversion and electron transfer.

Main Methods:

• Kinetic measurements
• Site-directed mutagenesis
• Electron paramagnetic resonance (EPR) spectroscopy
• UV/Vis spectroscopy
• X-ray crystallography

Main Results:

• Complex II enzymes (SQR and QFR) share a four-subunit architecture: two membrane-bound and two soluble subunits.
• A linear electron transfer chain facilitates efficient shuttling of reducing equivalents.
• Structural details governing reaction directionality and enzyme preference were identified.

Conclusions:

• The intricate structure of SQR and QFR supports distinct catalytic roles in respiration.
• Understanding these enzymes provides insights into fundamental bioenergetic processes.