The peroxidase/oxidase activity of soybean lipoxygenase--II. Triplet carbonyls and red photoemission during polyunsaturated fatty acid and glutathione oxidation.

During the aerobic reaction of soybean lipoxygenase with polyunsaturated fatty acids (linoleic, linolenic, and arachidonic acid) oxygen uptake is followed by excited carbonyl photoemission. The chemiluminescence yield of phi cl = 10(-10) photons/O2 molecule consumed is enhanced 2-3 orders of magnitude by the carbonyl sensitizers 9,10-dibromo-anthracene-2-sulfonate (kET tau 0 = 10(4) M-1; phi cl = 10(-8) photons/O2) and chlorophyll-a (kET tau 0 = 10(6) M-1; phi cl = 10(-7) photons/O2), respectively. alpha,beta-Saturated triplet excited carbonyls as from 1,2-dioxetane cleavage are discussed to arise from a secondary peroxidase/oxidase reaction with aldehydes formed in the course of enzymic lipid peroxidation. When 1 mM glutathione is added to the aerobic lipoxygenase/arachidonate reaction, carbonyl emission (375-455 nm) is replaced by intense red bands (630-645 nm and 695-715 nm) resembling the characteristic spectrum of (1 delta g)O2-singlet oxygen dimol-emission. The quantum yield (phi cl = 10(-8) photons/O2) remains unaffected by chlorophyll indicating that the red emission is independent of excited carbonyls. The effect of GSH is attributed to dioxetane interception and subsequent glutathione peroxidation generating 1O2 by electron transfer from the superoxide anion radical to a peroxysulfenyl radical.