In protein stabilizers like DTT and beta-mercapto-ethanol, this element is the reductant.
A hypervalent atom of this element is the lightest atom that can be found at the center of an octahedral compound. Penicillin and biotin contain heterocycles of nitrogen and this element. This element reduces iodine in the iodine clock reaction. This element forms a cluster with iron in proteins such as aconitase. In protein stabilizers like DTT and beta-mercapto-ethanol, this element is the reductant. In its most common allotrope, this element forms an eight-member ring. This element's most common oxidation state is negative 2, just like its upper neighbor on the periodic table, oxygen. For 10 points, name this element whose compounds often smell like rotten eggs.
A hypervalent atom of this element is the lightest atom that can be found at the center of an octahedral compound.
sulfur [or S]