Singlet Oxygen‐mediated Photobleaching of the Prosthetic Group in Hemoglobins and C‐Phycocyanin

Abstract

Proteins bearing colored prosthetic groups, such as the heme group in hemoglobin or the bilin group in c-phycocyanin, quench singlet oxygen by interactions at the apoprotein and the prosthetic group levels. In both proteins, chemical modification of the chromophore constitutes only a minor reaction pathway. While total deactivation of singlet oxygen takes place with rate constants of 4.0 x 10(9) and 4.2 x 10(8) M-1 s-1 for hemoglobin and phycocyanin, respectively, the bleaching of the chromophore takes place with rate constants of 3.2 x 10(6) and approximately 1 x 10(7) M-1 s-1. Irradiation of phycocyanin with red light bleaches the chromophore with low yields (approximately 0.8 x 10(-4)). Part of this bleaching is mediated by singlet oxygen produced by the irradiation of the bilin group. The low relevance of the singlet oxygen pathway is compatible with a low quantum yield (approximately 10(-3)) of free singlet oxygen production after irradiation of the protein.

C-Phycocyanin: A Biliprotein with Antioxidant, Anti-Inflammatory and Neuroprotective Effects

“…Over all the conditions employed it was observed that in excess of Pc, 0.16 ± 0.04 chromogenic groups were bleached per HOCl molecule introduced into the system, which implies that apoprotein moiety, and not the chromogenic groups, is the main target of the HOCl attack. In this regard, the behavior of Pc is similar to that reported for its reaction with singlet oxygen [27] and contrast with results obtained employing peroxyl radicals [19] or 2,2' azinobis (3-ethylbenzthiazoline sulfonic acid (ABTS) derived radicals (C. Aliaga unpublished results).…”

Nutraceutical properties of phycocyanin

“…In addition they described for the first time the anti-inflammatory properties of PC (Romay et al, 1998b). It took a little longer for other researchers worldwide to confirm previous results or to discover that PC scavenged singlet oxygen ( 1 O2) (Tapia, Galetovic, Lermp, Pino, & Eduardo, 1999), hypochlorous acid (HOCl) (Bermejo, Pinero, & Villar, 2008;Romay, Gonzalez, Pizarro, & Lissi, 2000), peroxyl radical (ROO • ) (Benedetti, Benvenuti, Scoglio, & Canestrari, 2010;Romay et al, 2000), • OH (Bermejo et al, 2008) (Thangam et al, 2013) and hydrogen peroxide (H2O2) (Fernαndez-Rojas et al, 2014) (Fig. 4).…”

“…Other assays have been used to determine the scavenging activity of PC including oxygen radical absorbance capacity (ORAC), ferrous ion oxidation xylenol orange (FOX), ferric reducing ability of plasma (FRAP) assay, reducing power assay and intracellular reactive oxygen levels using 2′,7′ dichlorofluorescein diacetate (DCFH-DA) (Madhyastha, Sivashankari, & Vatsala, 2009). During the scavenging activity of PC, its color gradually fades and its absorbance at 620 nm is reduced, its fluorometric intensity disappears and two new bands are observed at approximately 640 nm (Benedetti et al, 2004;Lissi et al, 2000;Patel et al, 2005;Tapia et al, 1999).…”

Influence of C-phycocyanin on hepatocellular parameters related to liver oxidative stress and Kupffer cell functioning

“…T 3 -induced TNF-a response is also suppressed by C-phycocyanin pretreatment, an effect that may be ascribed to the reduction in the respiratory burst activity of Kupffer cells exerted by the biliprotein. Inhibition of Kupffer cell respiration by C-phycocyanin coupled to its antioxidant properties [2,3] are likely to diminish the oxidative stress status at the liver macrophage level, which in turn may decrease the signal transduction pathway leading to an enhanced expression of redox-sensitive genes such as that coding for TNF-a [27,28]. TNF-a expression in macrophages is induced through activation of redox-sensitive transcription factors such as NF-kB [27,28], a response that is elicited by hydrogen peroxide derived from NADPH oxidase operation in the respiratory burst process [29].…”

“…This biliprotein exhibits an antioxidant behavior evidenced by its capacity to scavenge free radicals produced by different generating systems [2] and to quench singlet oxygen [3], probably by interactions at the apoprotein and/or the prosthetic group levels. In addition, C-phycocyanin also shows an anti-inflammatory activity in various in vitro and in vivo experimental models, that may be partly due to its antioxidant action [2,4,5].…”