![]() ![]() GSH peroxidases have been identified exclusively in eukaryotic cells ( 2), and although some bacteria synthesize GSH, these enzymes appear to be lacking in bacteria ( 16). Repair enzymes such as peroxidases, which convert peroxides to alcohols ( 18), receive electrons from partner NAD(P)H reductases ( 21, 38) or use either reduced glutathione (GSH) or thioredoxin (Trx) as an electron donor (in the case of thiol peroxidases) ( 18). Numerous enzymes are dedicated to the elimination or repair of damage caused by oxygen by-products. −) and hydrogen peroxide (H 2O 2), which can damage all cellular components ( 46).Oxygen, a strong oxidant, interacts with other environmental factors to form by-products like superoxide anion (O 2 The existence of a novel redox function that compensates for trxB1 deficiency is suggested.Īn aerobic environment is inevitably a source of cellular oxidative stress. lactis and that its inactivation triggers induction of several mechanisms acting at the membrane and metabolic levels. This study showed that thioredoxin reductase is not essential in L. Unexpectedly, a decrease specific to the oxidized, inactive form was observed in the trxB1 mutant, possibly because of proteolysis of oxidized GapB. lactis differed by the oxidation state of catalytic-site cysteine C 152. ![]() We determined that the two GapB isoforms in L. Two additional effects of trxB1 were not previously reported in other bacteria: (i) induction of proteins involved in fatty acid or menaquinone biosynthesis, indicating that membrane synthesis is part of the cellular response to a redox imbalance, and (ii) alteration of the isoforms of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GapB). Proteomic analyses showed that known oxidative stress defense proteins are induced in the trxB1 mutant. Aerobic growth of the trxB1 mutant did not require glutathione, also ruling out the need for this redox maintenance system. Unexpectedly, the trxB1 mutant was viable without DTT and under aerated static conditions, thus disproving the essentiality of this system. The mutant was obtained under anaerobic conditions in the presence of dithiothreitol (DTT). Some gram-positive bacteria, including Lactococcus lactis, do not produce glutathione, and the thioredoxin system is presumed to be essential. Thiol-disulfide bond balance is generally maintained in bacteria by thioredoxin reductase-thioredoxin and/or glutathione-glutaredoxin systems. ![]()
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