Streptococcus faecalisにおけるピルビン酸酸化とそれに関連する代謝に関する研究-5-脂質欠乏培地における菌の増殖に及ぼすアスコルビン酸および2価鉄イオンの効果

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Ascorbic acid or FeSO4 permitted the growth of Streptococcus faecalis 1OC1 in a semisynthetic medium lacking lipid components. The oxidation-reduction potential (ORP) of the medium was markedly lowered by the addition of these substances, whereas ORP of the medium supplemented with other growth-permitting substances such as lipoic acid or sodium acetate remained unchanged at high levels during the lag phase of growth. This fact suggests that ascorbic acid and FeSO4 would enable the bacterial growth by giving reducing environments to the medium. Both ascorbate and FeSO4, however, did not have influences on the NADH oxidase activity of cell-free extracts of this organism, indicating that the dissolved oxygen in the medium is not consumed and the formation of hydrogen peroxide is not prevented by the addition of these compounds. On the other hand, hydrogen peroxide was decomposed effectively by the reductone or the ferrous ions. Furthermore, it was shown that the growth effect was not attributable to the stimulation of lipoic acid biosynthesis. These results strongly suggest that there may be a hydrogen peroxide-sensitive pyruvate dehydrogenation system, and that ascorbic acid and FeSO4 serve to eliminate the peroxide which is known to be formed by NADH oxidation and accumulated in this organism lacking cytochrome pigments and catalase.
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