Oxygen and toxicity inhibition of amino acid biosynthesis

Abstract

ALTHOUGH oxygen is of therapeutic benefit for various human diseases, its usefulness is limited by its toxicity^1,2. In spite of progress, the cause of the convulsions observed in humans and other animals exposed to hyperbaric oxygen remains unknown^3,4, and the biochemical basis of the lung damage resulting from chronic exposure to increased oxygen tensions is poorly understood⁵. Oxygen toxicity, although necessarily expressed in different ways, affects various life forms from bacteria to man^3,4. There is considerable theoretical basis and experimental evidence for mechanisms of toxicity shared at the cellular and subcellular levels, and research on basic sites of toxicity has often involved tissue cultures or bacteria². The growth and respiration of Escherichia coli is rapidly, but reversibly, inhibited by hyperbaric oxygen in minimal salts medium⁶. Significant protection for some microbes against the growth-inhibitory effects of hyperbaric oxygen has been obtained with nutritional supplements, including yeast extract⁷. We have now found that E. coli E-26, the source of which has been identified previously⁶, is protected from oxygen toxicity by yeast extract because of its amino acid content: a mixture of 20 amino acids gave similar protection.