Oxygenation of (3Z)-Alkenals to 4-Hydroxy-(2E)-Alkenals in Plant Extracts: A Nonenzymatic Process

Abstract

There is large interest in 4-hydroxy-(2E)-alkenals because of their cytotoxicity in mammals. However, the biosynthetic pathway for these compounds has not been elucidated yet. In plants, 4-hydroxy-(2E)-alkenals were supposed to be derived by the subsequent actions of lipoxygenase and a peroxygenase on (3Z)-alkenals. The presence of 9-hydroxy-12-oxo-(10E)-dodecenoic acid (9-hydroxy-traumatin) in incubations of 12-oxo-(9Z)-dodecenoic acid (traumatin) in the absence of lipoxygenase or peroxygenase, has prompted us to reinvestigate its mode of formation. We show here that in vitro 9-hydroxy-traumatin, 4-hydroxy-(2E)-hexenal and 4-hydroxy-(2E)-nonenal, are formed in a nonenzymatic process. Furthermore, a novel product derived from traumatin was observed and identified as 11-hydroxy-12-oxo-(9Z)-dodecenoic acid. The results obtained here strongly suggest that the 4-hydroxy-(2E)-alkenals, observed in crude extracts of plants, are mainly due to autoxidation of (3Z)-hexenal, (3Z)-nonenal and traumatin. This may have implications for the in vivo existence and previously proposed physiological significance of these products in plants.

Lipoxygenases and their metabolites in formation of plant stress tolerance

“…Meanwhile, the enzyme is on the membrane or transported to a wounded site. One of the versions is the presence of the HPL predecessor that is activated after cutting of the N-ter- [65]. 13-hPL genes expression was detected in the plant overground part while that of 9-HPL -in the root one.…”

Routes to 4-Hydroxynonenal: Fundamental Issues in the Mechanisms of Lipid Peroxidation

“…In observing the facile oxidation of 3Z-nonenal to 4-HPNE, we were prompted to propose a non-enzymatic pathway consisting of autoxidative formation of 9-HPODE from linoleic acid, followed by a Hock-type cleavage to give 3Z-nonenal, which undergoes rapid oxidation into 4-HPNE (12). It was shown that a route via 3Z-nonenal could account for HNE production in plant tissues (18). We surmised that the acid-catalyzed Hock cleavage could be achieved by the fatty acid carboxylate or other acidic moieties present under * This work was supported, in whole or in part, by National Institutes of Health Grants GM15431 and GM076592.…”

Gradual Soil Water Depletion Results in Reversible Changes of Gene Expression, Protein Profiles, Ecophysiology, and Growth Performance in Populus euphratica, a Poplar Growing in Arid Regions

“…ROS lead to the oxidation of unsaturated fatty acids in membranes, yielding LOOH (Taylor et al, 2004). These hydroperoxides are degraded nonenzymatically and cause the formation of carbonyl compounds, many of which are aldehydes (Noordermeer et al, 2000;Schneider et al, 2001). The moderate increases in MDA and LOOH were, therefore, indicating moderate oxidative stress.…”