Antioxidant Properties of Plastoquinol and Other Biological Prenylquinols in Liposomes and Solution

Abstract

Oxidation of biological prenylquinols, like plastoquinol-9 (PQH₂-9), ubiquinol-10 (UQH₂-10), reduced vitamins K₁(VK₁H₂) and K₂(VK₂H₂), α-tocopherol quinol (α-TQH₂) and α-tocopherol (α-T) was followed by their fluorescence during sonication of egg yolk lecithin/prenylquinol liposomes. The order of magnitude of oxidation of the prenylquinols by free radicals generated during sonication was <UQH₂-10> VK₂H₂ VK₁H₂ α-TQH₂ <PQH₂-9> α-T. It was shown that egg yolk lecithin undergoes degradation even when sonicated briefly under atmosphere of nitrogen and at 0°C. A kinetic study of free radical scavenging action of the prenylquinols in solvents of different polarity was performed. The pseudo-first-order rate constants, k, for the reaction of the prenylquinols with 1,1-diphenyl-2-picryl-hydrazyl (DPPH) in hexane showed that their scavenging activity changes in the order <VK₂H₂ VK₁ H₂ <α-TQH₂ PQH₂-9> α-T> UQH₂-10, being the highest in hexane and methanol, whereas in acetone and ethyl acetate the scavenging activity appeared much lower. The reaction rate constants, k, were apparently not dependent on the solvent polarity. The antioxidant activity of the prenylquinols in natural membranes is discussed.

Key Words:

• Antioxidant activity
• Plastoquinol
• Prenylquinol
• Free radical
• Sonication
• Liposome