Under these conditions sulphoacetaldehyde was generated at a constant rate of 637+/-18 pmol/h per ml for over 7 h. Activation of human neutrophils (1.67 x 10(6) cells/ml) with latex beads resulted in a respiratory burst of oxygen-radical production, the products of which were partially sequestered by 12.5 mM taurine. There was no detectable formation of sulphoacetaldehyde when taurine itself was incubated with the tissue homogenates under the same conditions. This activity was found to be lost on heat denaturation, but retained after dialysis. Rat liver homogenates accelerated this decay in a process that was proportional to tissue-protein concentration and saturable, with maximum velocity (Vmax) and Km values of 0.28+/-0.01 nmol/min per mg of protein and 37+/-9 microM respectively. N-Chlorotaurine ( taurine chloramine), formed by treating taurine with hypochlorous acid, was shown to decompose to sulphoacetaldehyde with a first-order rate constant of 9.9+/-0.5 x 10(-4).h-1 at 37 degrees C in 0.1 M phosphate buffer, pH 7.4. These results indicate that Tau-NHCl can serve as an oxidant reservoir, exhibiting either delayed oxidant effects or acting as an oxidant at a distant site.Ĭonversion of taurine into N-chlorotaurine ( taurine chloramine) and sulphoacetaldehyde in response to oxidative stress.
However, when NH4+ was added to the medium, Tau-NHCl oxidizes IkappaB and inhibits NF-kappaB activation, probably through oxidant transfer to NH4+ leading to NH2Cl formation. Accordingly, NH2Cl oxidizes cytosolic proteins, such as IkappaB, and inhibits NF-kappaB activation, whereas Tau-NHCl exhibits no comparable effect. In contrast, membrane-permeable ammonia mono- chloramine (NH2Cl) has a half life of only 6 min. When Tau-NHCl was added to Jurkat cells in suspension, its half life was about 75 min. When PMNs were stimulated in PBS lacking taurine, extracellular oxidant concentration was low, but the concentration increased 3-4 fold when 15 mM taurine was added, indicating that taurine lowers oxidant levels inside the cell. Taurine is abundant in polymorphonuclear leukocytes (PMNs) where it reacts with PMN-derived hypochlorous acid to form taurine chloramine (Tau-NHCl), a substance that does not readily cross the cell membrane.
Ogino, Tetsuya Than, Tin Aung Hosako, Mutsumi Ozaki, Michitaka Omori, Masako Okada, Shigeru Taurine chloramine: a possible oxidant reservoir.
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