1. α-トコフェロールおよびカロテノイドのリン脂質膜における存在様態と一重項酸素不活化反応のキネティクス
Kinetics and Dynamics of α-Tocopherol and Carotenoids for Deactivating Singlet Oxygen in Phospholipid Membranes

Kenji FUKUZAWA, Akira TOKUMURA
2001 VITAMINS  
The singlet oxygen ('O,) deactivating rate constants (k,) of ct-tocopherol (a-Toc) and caretenoids such as Pcarotene, astaxanthin and canthaxanthin and their inhibiting activities for 'O,-dependent lipid peroxidation (ICso, that is, the concentration required for 50% inhibition ef lipid peroxidation) were investigatecl in liposomes and compared to those in EtOH solution. Liposomes were prepared from dimyristoylphosphatidylcholine to rneasure the k, and egg yolk phosphatidylcholine to measure
more » ... IC. values. 'Oi was generated by photoirradiation using three photosensitizers, Rose bengal and methylene blue, which generate 'O, at the membrane surface or in bulk water, and 2-(l-pyrene) dodecanoic acid, which generates 'Oi in the membrane hydrophobic inner region. The k, values were determined in membranes considering the fo11owing two points: O antioxidants exist in and IC 50 rnembranes and their active moieties are distributed in different regions of membranes at different concentrations; @dynarnics of iO, in membranes (generation site of 'O, depending on the localization of photosensitizer in membranes, and so]ubility of 'O, which differs in the site of membranes). In conclusion, the fol)owing three factors are experimentally confirmed to be important for the consideration of 'O, deactivating activities of a-Toc and carotenoids in mernbranes:(D the concentration ef antioxidants (EtOH solution < membrane), especially the local concentration of their active moieties in membranes (in the case of OH-group of a-Toc, O%, 50-60%, apd 40-50% at polar zone, hydrogen belt, and hydrophobic core, respectively, of the membranes); @ the mobility of antioxidants (EtOH solution > membrane), the mobility of membrane phospholipid (liquid crystalline state > gel state), the mobility of antioxidants in membranes (antioxidants located at one half of the bilayer membrane such as ct-tocophero1 > antioxidants located across the bilayer such as P-carotene; antioxidants interactive with polar head group of lipid in membrane such as astaxanthin < antioxidants nointeractive with polar head group of lipid in membrane such as P-carotene), and the local mobility of their active rnoieties (in case of OH-group of a-Toc. rnembrane surface < membrane inner region); @the dielectric constant (micropolarity) at the domains in membranes. that is higher in membrane surface than in membrane inner region, where the active moieties of antioxidants deactivate iO, (in case of ct-Toc, reactivity is high in the solution with high dielectric constant).
doi:10.20632/vso.75.1_1 fatcat:jsqhdwbffjhvzl5up4mhislbo4