Review: on the chemistry of oxidative stress.

Injury of plant cells as well as mammalian cells is connected with the activation of 'dormant' lipoxygenases. In the presence of oxygen, these enzymes are activated and enabled to catalyze the formation of hydroperoxides of linoleic and other polyunsaturated fatty acids. Reactivity of dormant lipoxygenases seems to be dependent on the carbon number between the alkyl end and the double bond situated next to this end in an unsaturated acid. In contrast to these dormant lipoxygenases there exists a second group of lipoxygenases, which are active in plant cells all the time, independent of an injury. They react mainly with acids possessing two homoconjugated double bonds within a distance of seven CH2 groups from the carboxylic end. Thus, they 'count' from the reverse end of the molecule. These lipoxygenases produce F-acids. They are converted, when plant cells are injured by hydroperoxides produced from unsaturated acids, into dioxoenoic acid intermediates which probably are used for defense. In mammalian tissues, lipoxygenases produce in the case of cell injury plasmalogen epoxides. These are analogous to dioxoenoic acids' highly reactive intermediates (in a chemical sense) which react immediately with nucleophiles. Such transformation of plasmalogens may be responsible for the development of chronic diseases, e.g., atherosclerosis, Alzheimer's disease and also for aging.