Kinetic Studies of Lipid Oxidation Induced by Hemoglobin Measured by Consumption of Dissolved Oxygen in a Liposome Model System

The effect of hemoglobin (Hb) and lipid concentration, pH, temperature, and different antioxidants on heme-mediated lipid oxidation of liposomes from marine phospholipids was studied. The rate of lipid oxidation was measured by consumption of dissolved oxygen. Heme-mediated lipid oxidation at different Hb and lipid concentrations was modeled by Michaelis-Menten kinetics. The maximum rate (V-max) for the reaction with cod and bovine Hb as a pro-oxidant was 66.2 +/- 3.4 and 56.6 +/- 3.4 mu M/min, respectively. The Michaelis-Menten constant (K-m) for the reaction with cod and bovine Hb was 0.67 +/- 0.09 and 1.2 +/- 0.2 mu M, respectively. V-max for the relationship between the oxygen uptake rate and lipid concentration was 43.2 +/- 1.5 mu M/min, while the K-m was 0.93 +/- 0.14 mg/mL. The effect of the temperature followed Arrhenius kinetics, and there was no significant difference in activation energy between cod and bovine Hb. The rate of lipid oxidation induced by bovine Hb was highest around pH 6. Ethylenediaminetetraacetic acid (EDTA) had no significant effect on heme-mediated lipid oxidation, but alpha-tocopherol and astaxanthin worked well as antioxidants. Kinetic differences were found between iron and Hb as pro-oxidants, and the efficacy of the antioxidants depended upon the pro-oxidant in the system.