Question

"Cu, Zn, SOD concers O2.- into oxygen and HOOH. Which amino acid in the active site binds the metals, what is the role of Zn and Cu, and why is the enzymatic process required given that spontaneous dismutation does occur?

Answer 1

Histidine residues in the active site bind copper and zinc in superoxide dismutase, which catalyzes the dismutation of superoxide radicals.

Step-by-step explanation:

The enzyme superoxide dismutase (SOD) involves the conversion of superoxide radicals (O2.-) into molecular oxygen (O2) and hydrogen peroxide (H2O2). In the active site of SOD, the amino acid histidine is responsible for binding the metal ions zinc (Zn) and copper (Cu). Zn plays a role in stabilizing the enzyme structure, while Cu participates in redox reactions to facilitate the dismutation process.

Although spontaneous dismutation of superoxide radicals does occur, the enzymatic process is required because it is much more efficient. Enzymes like SOD increase the rate of reactions to a level that is consistent with the needs of the cell, which spontaneous reactions cannot achieve at the same rate. The presence of metal ions such as Zn and Cu aids in the optimal performance of these enzymatic reactions. Zn, as a Lewis acid, can stabilize the transition state and participate in group transfer reactions, while Cu can rapidly transfer electrons due to minimal structural reorganization between its oxidized and reduced states.