Mechanisms Responsible for the Antioxidant Properties of Chlorophyllin: a Pulse Radiolysis Study

Chlorophyllin, the water-soluble analogue of the ubiquitous green pigment chlorophyll has been shown to be a potent antioxidant and radioprotector under both in vitro and in vivo conditions. It is a potent protector of membrane damage and prevents protein oxidation, lipid peroxidation besides depletion of thiols induced by radiation, photosensitization and other oxidants. To analyze the possible mechanisms involved, we have studied the reaction of chlorophyllin with biologically relevant radical species in the form of linoleic acid peroxyl radical (LOO), chloroperoxyl radical (CCl3O2), azide radical (N3) and thiyl radical (RS). The summary of results obtained are given below: Pulse radiolysis studies show that these radicals (CCl3O2, N3, RS) react with chlorophyllin in a similar way producing transient absorption bands at 370 nm and in the region of 430-450 nm with bleaching at 410 nm. The one electron oxidized species was long lived without any decay upto 1 millisecond. The high rate constant values reveal that chlorophyllin is able to scavenge these radicals effectively. However, the reaction of LOO radical with chlorophyllin was slow and the yield of one-electron oxidized species of chlorophyllin was also small. This indicates that inhibition of lipid peroxidation observed with chlorophyllin may involve other mechanisms.