Nitric oxide binding to oxygenated hemoglobin under physiological conditions

Area of Science:

• Biochemistry
• Physiological Chemistry

Background:

• Nitric oxide (NO) plays a crucial role in various physiological processes.
• The reaction between NO and hemoglobin (Hb) is critical for understanding NO bioavailability and its effects.
• Previous studies proposed that NO preferentially forms nitrosyl hemoglobin (HbNO) over methemoglobin (metHb) at high oxygen saturation.

Purpose of the Study:

• To investigate the formation of HbNO and methemoglobin (metHb) when NO is added to hemoglobin under varying oxygen saturation levels.
• To determine if oxygen saturation influences the reaction kinetics of NO with hemoglobin.
• To re-evaluate previous findings on the reaction products of oxyhemoglobin with NO.

Main Methods:

• Addition of nitric oxide (NO) to hemoglobin solutions in phosphate buffers (0.1 M and 0.01 M) and to whole blood.
• Systematic variation of hemoglobin oxygen saturation levels.
• Quantification of nitrosyl hemoglobin (HbNO) and methemoglobin (metHb) formation.

Main Results:

• The formation of both HbNO and methemoglobin (metHb) proceeded at rates independent of hemoglobin oxygen saturation across all tested conditions.
• These findings were consistent in phosphate buffers and whole blood.
• The observed kinetics contradict a previous report suggesting elevated HbNO formation at high oxygen saturation.

Conclusions:

• The reaction kinetics of NO with hemoglobin, leading to HbNO and metHb formation, are not significantly influenced by oxygen saturation.
• The previously proposed model requiring a "radical rethink" of NO-hemoglobin interactions under physiological conditions is not supported by these results.
• The formation of methemoglobin and nitrosyl hemoglobin occurs independently of oxygen saturation levels.