Kinetics of phycocyanine bilin groups destruction by peroxyl radicals

Bilin groups in c-phycocyanine are readily bleached by peroxyl radicals pro duced in the thermolysis of 2,2'-azobis(2-amidinopropane). From an evaluati on of the bilin groups destroyed per radical that interacts with the protei n, it is concluded that the bilin moiety is the main target of the radicals . Kinetic expressions are derived that allows an estimation of the substrat e reactivity from the analysis of the rate of bilin group modification as a function of the protein concentration. From this analysis it is concluded that micromolar concentrations of c-phycocyanine are able to reduce the ste ady state concentration of the peroxyl radicals by one half, indicating a h igh antioxidant activity for this compound. This conclusion is confirmed by measuring the capacity of the protein to protect 1-naphthol from modificat ion by peroxyl radicals. The results obtained show that the bilin groups ha ve, on a molar basis, an antioxidant activity similar to that of potent ant ioxidants such as catechin. (C) 2000 Elsevier Science Inc.