Singlet molecular oxygen in the Haber-Weiss reaction.

Abstract

Characteristic chemiluminescence emission of singlet ('Ag) molecular oxygen at 1268 nm is reported from a Haber-Weiss reaction. The reaction consists of mixing aqueous hydrogen peroxide with a solution of potassium superoxide, solubilized by 18-crown-6 ether in carbon tetrachloride or in dry acetonitrile at room temperature. Since the discovery of the enzyme superoxide dismutase by J. M. McCord and I. Fridovich [(1968) J. Biol. Chem. 243, 5733-5760], the identity of the reactive oxidant in superoxide-generating systems in biology has remained a chemical mystery. The results presented here suggest strongly that the reactive species is singlet oxygen generated via the Haber-Weiss reaction and not, as usually assumed, the hydroxyl radical, -OH, generated by the same reaction.matic systems, the proposal has met with almost universal acceptance and forms the foundation of this very active research field. The spectroscopic data presented here, however, show the characteristic 1268-nm chemiluminescence emission spectrum of singlet molecular oxygen, in the reaction of superoxide anion with hydrogen peroxide. This experiment constitutes direct evidence of the generation of singlet dioxygen in the Haber-Weiss reaction and suggests this species as a possible reactive oxidant in the reaction. This result strongly suggests singlet oxygen could be the sought-after in vivo reactive species. Experimental Results in Carbon Tetrachloride Solutions Superoxide Dismutase (SOD) MechanismsThe enzyme SOD has come to be regarded as a major participant in the antioxidative defense of the host system. The enzyme is both constitutive and inducible under oxidative stress. SOD catalyzes the conversion of superoxide anion to H202 and the dioxygen molecule (1). The enzyme is a strong catalyst and is ubiquitous, even though the uncatalyzed dismutation of O2 is already a fast reaction (107 M-1s-1) under physiological conditions. The superoxide anion, moreover, has proven to be relatively unreactive toward most biological components (2). The question becomes, What then is the biological oxidant generated from superoxide anion in vivo that this enzyme protects against? Based on chemical product and luminescence sensitization studies using potassium superoxide, it was proposed (3) that SOD protects the host system by preventing the generation of the highly reactive long-lived diffusible singlet oxygen molecule O2(1Ag) from superoxide anion. Spectroscopic evidence has established the generation of singlet oxygen in the (i) water-induced dismutation of superoxide anions (4, 5) and (ii) in the electron transfer reactions of superoxide anion with metal redox systems (6, 7). A different interpretation was offered by Beauchamp and Fridovich (8), who in an attempt to rationalize the in vivo role of SOD, proposed that the reactive intermediate was the highly reactive hydroxyl radical generated by the reaction of superoxide anion with hydrogen peroxide-the classic Haber-Weiss reaction (9). They based their suggestion on the inhibitory effects of the...

Singlet Oxygen Signatures Are Detected Independent of Light or Chloroplasts in Response to Multiple Stresses

“…However, the existence of such specialized sources is unknown in plants. Superoxide can react with H 2 O 2 via a Haber-Weiss mechanism to form singlet oxygen (H 2 O 2 +O 2 2 → OH 2 + OH$ + 1 O 2 ; Kellogg and Fridovich, 1975;Khan and Kasha, 1994), although the efficiency of singlet oxygen production by these ROS in vivo is not known (MacManus-Spencer and McNeill, 2005). Nonetheless, the accumulation of superoxide and H 2 O 2 is readily detected in local or systemic wounded tissue (Sagi et al, 2004;Warwar et al, 2011) and in the immune responses (Dubiella et al, 2013).…”

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“…This is rapidly converted to hydrogen peroxide (H 2 O 2 ). Both of the mentioned molecules react by producing singlet oxygen (4,5).…”

“…Moreover one singlet oxygen molecule can be produced by either the reaction of one hydroxyl radical and a superoxide or two superoxide ions and two hydrogen ions (5), shown in the Eqs. [2] and [3], respectively.…”

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