L Jl Jl J

Rod Core Rod

FIGURE 6.1 Schematic representative of one type of phycobilisome. (Modified from MacColl, R., Biochimica et biophysica acta, 1657, 73-81, 2004; L.-N. Liu et al., Biochimica et biophysica acta, 1708, 133-142, 2005.)

by thioether bonds to the cysteine residues. Allophycocyanin (APC), phycocyanin (pc), phycoerythrin (PE), and phycoerythrocyanin (PEC) are the four basic classes of phycobiliproteins in supermolecular phycobilisomes. Electron microscopic and crys-tallographic studies have elucidated the general architecture of this macromolecular assembly. It comprises high affinity a- and j-subunit polypeptides, which commonly associate with each other to form (aj)3 or (aj)6-monomers. Figure 6.1 schematically depicts one phycobilisome with a three-cylinder core. The antennae rods of phycobil-isomes consist of APC at the core, C-phycocyanin (Cpc) in the middle (blue), and PE/PEC at the tip (pink).35,36 Their collective range of absorption covers the entire visible spectrum of sunlight, with an overall energy transduction efficiency that exceeds 95%, such that the energy proceeds in the direction from tip to the core through PE/PEC, Cpc, APC, and finally to the reaction center.

Effect of Phycocyanin on Lipid Peroxidation

Lipid peroxidation can be defined as the oxidative deterioration of lipids that contain carbon-carbon double bonds. Lipid hydroperoxides are nonradical intermediates that are derived from unsaturated fatty acids, phospholipids, glycolipids, and cholesterol esters. Lipid hydroperoxides may be formed in enzymatic or nonenzymatic reactions that are mediated by "reactive oxygen species" (ROS), which are responsible for the destruction and damage of cell membranes. These ROS include hydroxyl radicals, lipid oxyl or peroxyl radicals, as well as singlet oxygen and peroxinitrite that are formed from nitrogen oxide (NO). All of these groups of atoms are frequently byproducts of oxygen metabolism, behaving as a unit, called a free radical.

Various investigations have verified that phycocyanin scavenges free radicals because its open chain tetrapyrroles structure. Phycocyanin has been observed to be able to inhibit liver microsomal lipid peroxidation that is induced by Fe+2-ascorbic acid.25,26 The group25,26 that presented that observation also reported that phycocy-anin reduced significantly (p < .05) and in a dose-dependent manner ear edema in mice that was induced by arachidonic acid and tetradecanoylphorbol acetate, as well as carrageenan-induced rat paw edema (both in intact and adrenalectomized animals).25,26 Furthermore, C-phycocyanin (from S. platensis) effectively inhibited

CCl4-induced lipid peroxidation in rat liver in vivo. Both native and reduced phycocy-anin substantially suppressed peroxyl radical-induced lipid peroxidation in rat liver microsomes. The inhibition depended on the concentration, with an IC50 of 11.35 and 12.7 ^M, respectively.11 Several works have clearly suggested that phycocyanin exhibits anti-inflammatory activity in experimental animal models of inflammation, and its antioxidative and oxygen free radical-scavenging properties may contribute, at least partially, to its anti-inflammatory activity.25'26

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