ABSTRACT
Sulfur-sulfur bonds are the backbone of biochemistry. Often, they have a structural role, involved in the maintenance of protein shape and function, as in keratin (Ogawa 1989). Disulfide groups confer unique properties as they can hold the whole molecule in a fixed conformation. However, this relatively rigid frame exists in a state of dynamic equilibrium, where formation of mixed disulfides with small molecules such as cysteine or glutathione (?-glutamyl-cysteinyl-glycine) will break the intramolecular bonding and disrupt the protein structure. The dual requirement for strong bonds which are readily made and equally readily disassembled leads to continuous formation and reformation of sulfur-sulfur bonds, and is essential for biochemical function (Kim 1992). Proteins may also act in transmission of molecular signalling. In this latter case, the disulfide bond, -S-S-, engages in a series of interconversions, breaking and remaking
the sulfur bonds to form heterodimers with other molecules often via reduction to thiols (-SH). The loosely-held electrons in the outermost orbitals of the sulfur atoms confer a certain ‘flexibility’ to the electronic configuration, increasing the possibility of reactions with other sulfur-containing molecules, so that protein-protein and ligand-receptor links can be made rapidly.
