Question

When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe^2+ are occupied by___________

(a) One O atom and one amino acid atom

(b) One O2  molecule and one amino acid atom

(c) One O2  molecule and one heme atom

(d) Two O atoms

The question was posed to me in an online interview.

The query is from Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins in chapter Three Dimensional Structure Of Proteins and Protein Function of Biochemistry

Answer 1

Correct option is (b) One O2  molecule and one amino acid atom

To explain: The two coordination bonds to Fe^2+ perpendicular to the porphyrin ring system. One of these bonds is occupied by a Hys residue and the other bond by O2.