Rationalization of properties of nitrate reductases in Rhodopseudomonas capsulata
Rationalization of properties of nitrate reductases in Rhodopseudomonas capsulata
复制标题
荚膜红假单胞菌硝酸盐还原酶性质的合理化
DOI：
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发表时间：
1984
影响因子：
2.8
通讯作者：
S. Ferguson
中科院分区：
文献类型：
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作者：
A. McEwan;J. Jackson;S. Ferguson
摘要1.比较了以硝酸盐为唯一氮源的光营养培养的几株胶囊红假单胞菌的硝酸还原酶活性。2.菌株AD2和BK5与自发突变株N22DNAR+相似(由McEwan等人描述)。1982年FEBS Lett.150,2772-280)，硝酸盐的还原被光照或氧气抑制，但不受NH4+的抑制，在黑暗厌氧条件下流向硝酸盐的电子产生了细胞质膜电位(根据内源类胡萝卜素吸收光谱的电致变色位移来判断)。相反，菌株N22和St.Louis悬浮液中硝酸盐的消失依赖于光照，并受到NH4+的抑制。N22、St.Louis和Kbl.3菌株不能在黑暗中加入硝酸盐产生膜电位。硝酸还原酶位于菌株AD2和突变体N22DNAR+的周质间隙中。AD2和N22DNAR+细胞的硝酸还原酶活性对叠氮相对不敏感，需要0.5 mM叠氮才能抑制50%。菌株BK5的硝酸还原酶与细胞膜的相关性较强，目前尚不能确定其定位于周质还是胞质表面。在BK5细胞中，硝酸还原酶活性对低浓度叠氮(2 GMM叠氮抑制50%)很敏感。推测菌株AD2、BK5和N22DNAR+的硝酸还原酶活性在功能上具有相同的作用。这些作用被认为包括：(I)硝酸盐同化的第一步。(Ii)提供一种替代氧的电子受体来产生膜电位。(Iii)一种处理过量还原当量以维持平衡生长的机制。这种类型的硝酸还原酶，特别是在AD2和N22DNAR+中，似乎类似于RPS反硝化菌株中描述的类型。球状芽孢杆菌，但与其他细菌中的膜结合细菌明显不同，包括反硝化的反硝化副氮假单胞菌和大肠杆菌。在以硝酸盐为氮源生长的厌氧光营养培养中，只有一种同化硝酸还原酶存在，该酶在完整细胞中的活性对叠氮相对敏感。由于这种还原酶在细胞破裂后无法被检测到，因此无法得出其在细胞中的位置的结论。
Abstract1.The properties of nitrate reductase activities have been compared in several strains of Rhodopseudomonas capsulata grown phototrophically in the presence of nitrate as sole nitrogen source.2.Strains AD2 and BK5 resemble the spontaneous mutant N22DNAR+ (described by McEwan et al. 1982 FEBS Lett. 150, 2772-280) in that reduction of nitrate was inhibited by either illumination or oxygen but not by NH4+, and that electron flow to nitrate under dark anaerobic conditions generated a cytoplasmic membrane potential (as judged by an electrochromic shift in the absorbance spectrum of endogenous carotenoid pigments). In contrast disappearance of nitrate from suspensions of strains N22 and St. Louis was dependent upon illumination and was inhibited by NH4+. Membrane potentials were not generated by addition of nitrate in the dark to N22, St. Louis or strain Kbl.3.Nitrate reductase was shown to be located in the periplasmic space of both strain AD2 and mutant N22DNAR+. The nitrate reductase activity in cells of AD2 and N22DNAR+ was relatively insensitive to azide, with 0.5mM azide required for 50% inhibition. The nitrate reductase of strain BK5 was more strongly associated with the cytoplasmic membrane and no conclusion could be reached about whether it was located on the periplasmic or cytoplasmic surface. In BK5 cells nitrate reductase activity was sensitive to low concentrations of azide (50% inhibition with 2 gmM azide). It is proposed that functionally the nitrate reductase activity in strains AD2, BK5 and N22DNAR+ has identical roles. These roles are suggested to include:(i)The first step in the assimilation of nitrate.(ii).Provision of an alternative electron acceptor to oxygen for generating a membrane potential.(iii).A mechanism for disposing of excess reducing equivalents in the maintenance of balanced growth.This type of nitrate reductase, especially in AD2 and N22DNAR+, appears to resemble that described in a denitrifying strain of Rps. sphaeroides, but to differ markedly from its membrane-bound counterpart in other bacteria including the denitrifying Paracoccus denitrificans and Escherichia coli.4.In other strains of Rps. capsulata including St. Louis, N22 and Kbl, only an assimilatory nitrate reductase, whose activity in intact cells is relatively sensitive to azide, is present in anaerobic, phototrophic cultures grown with nitrate as nitrogen source. As this reductase cannot be detected after breakage of cells, no conclusion can be made as to its location in the cell.