Related Experiment Video
Updated: Aug 30, 2026

Simultaneous Measurement of Superoxide/Hydrogen Peroxide and NADH Production by Flavin-containing Mitochondrial Dehydrogenases
Published on: February 24, 2018
The dual nature of human extracellular superoxide dismutase: one sequence and two structures
Steen V Petersen1, Tim D Oury, Zuzana Valnickova
1Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark.
Abstract:
Human extracellular superoxide dismutase (EC-SOD; EC 1.15.1.1) is a scavenger of superoxide anions in the extracellular space. The amino acid sequence is homologous to the intracellular counterpart, Cu/Zn superoxide dismutase (Cu/Zn-SOD), apart from N- and C-terminal extensions. Cu/Zn-SOD is a homodimer containing four cysteine residues within each subunit, and EC-SOD is a tetramer composed of two disulfide-bonded dimers in which each subunit contains six cysteines. The amino acid sequences of all EC-SOD subunits are identical. It is known that Cys-219 is involved in an interchain disulfide. To account for the remaining five cysteine residues we purified human EC-SOD and determined the disulfide bridge pattern. The results show that human EC-SOD exists in two forms, each with a unique disulfide bridge pattern. One form (active EC-SOD) is enzymatically active and contains a disulfide bridge pattern similar to Cu/Zn-SOD. The other form (inactive EC-SOD) has a different disulfide bridge pattern and is enzymatically inactive. The EC-SOD polypeptide chain apparently folds in two different ways, most likely resulting in different three-dimensional structures. Our study shows that one gene may produce proteins with different disulfide bridge arrangements and, thus, by definition, different primary structures. This observation adds another dimension to the functional annotation of the proteome.
Related Concept Videos
The Supercomplexes in the Crista Membrane
Electron Transport Chain: Complex III and IV
Ligand Binding and Linkage
Allosteric Proteins-ATCase
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
Gene Families
Occasionally these regions can be adapted to take on new roles within the organism, becoming novel genes...
Protein and Protein Structure
A protein's shape is critical to its function. For example, an enzyme can...
