Sulfide Quinone Reductase Like Protein (SQRDL)

A key enzyme in maintaining sulfide homeostasis is the sulfide quinone oxidoreductase (SQR), a ubiquitous protein present in all domains of life except plants. The SQRs have a monomeric molecular mass of around 50 kDa and have been described as dimeric membrane-associated proteins harboring 1 noncovalently bound FAD cofactor per monomer. Type I SQRs are found in many bacterial species, including A. aeolicus,and are involved in the cellular respiration pathway or in anaerobic photosynthesis. They have high catalytic rates and micromolar substrate affinities. Type II SQRs occur in other bacterial species and in many eukaryotes (where the enzyme is denoted by the acronym SQRDL). SQRDL gene is also present in humans, where it could help regulate the cellular sulfide concentration, thus influencing the processes of sulfide signaling.