Enzymatic Elimination of Hydrogen Peroxide by a Methemoglobin/L-Tyrosine System

Abstract

We studied the peroxidase activity of ferrylhemoglobin radical (Hb(Fe⁴⁺ = O*)) generated by the reaction of metHb (Hb(Fe³⁺)) with hydrogen peroxide (H₂O₂). To clarify the behaviors of ferrylHb radical, it was isolated from the reaction mixture of metHb and H₂O₂ by GPC at 4°C. The radical species underwent rapid autoreduction to metHb at 37°C accompanied with denaturation; however, it was stable for several minutes at 4°C. In ESR measurements, the signal of the ferrylHb radical immediately disappeared in the presence of l-Tyrosine (l-Tyr), and simultaneously, the signal of the ferric heme increased. This suggested that the ferrylHb radical immediately converted to metHb by l-Tyr even at 4°C. Furthermore, dimerized l-Tyr was detected in the reaction mixture. This showed that the ferrylHb radical was reduced to metHb by electron donation from l-Tyr. The enzymatic reaction using l-Tyr as the substrate resulted in the elimination of H₂O₂ in this system.

Keywords:

• Ferrylhemoglobin radical
• Hemoglobin vesicle
• Hydrogen peroxide
• L-Tyrosine
• Methemoglobin
• Peroxidase activity