Solomonson L P, Vennesland B
Forschungsstelle Vennesland der Max-Planck Gesellschaft, Berlin 33, Germany.
Plant Physiol. 1972 Oct;50(4):421-4. doi: 10.1104/pp.50.4.421.
A study of the growth-inhibiting effect of chlorate on the Berlin strain of Chlorella vulgaris Beijerinck provided complete confirmation of the theory of chlorate toxicity first proposed by Aberg in 1947. Chlorate was toxic to the cells growing on nitrate, and relatively nontoxic to the cells growing on ammonium. The latter cells contained only 0.01 as much NADH-nitrate reductase as the nitrate-grown cells. Chlorate could substitute for nitrate as a substrate of the purified nitrate reductase with Km = 1.2 mm, and V(max) = 0.9V(max) for nitrate. Bromate, and to a much smaller extent, iodate, also served as alternate substrates. Nitrate is a reversible competitive inhibitor of chlorate reduction, which accounts for the partial reversal, by high nitrate concentrations, of the observed inhibition of cell growth by chlorate. During the reduction of chlorate by NADH in the presence of purified nitrate reductase, there was a progressive, irreversible inhibition of the enzyme activity, presumably brought about by the reduction product, chlorite. Both the NADH-nitrate reductase activity and the associated NADH-cytochrome c reductase activity were inactivated to the same extent by added chlorite. The spectral properties of the cytochrome b(557) associated with the purified enzyme were not affected by chlorite. The inactivation of the nitrate reductase by chlorite could account for the toxicity of chlorate to cells grown on nitrate, though the destruction of other cell components by chlorite or its decomposition products cannot be excluded.
一项关于氯酸盐对普通小球藻柏林品系生长抑制作用的研究，完全证实了阿贝格于1947年首次提出的氯酸盐毒性理论。氯酸盐对以硝酸盐为氮源生长的细胞有毒，而对以铵盐为氮源生长的细胞相对无毒。后一种细胞所含的NADH-硝酸还原酶仅为以硝酸盐为氮源生长的细胞的0.01倍。氯酸盐可以替代硝酸盐作为纯化硝酸还原酶的底物，其米氏常数Km = 1.2 mM，最大反应速度V(max)为硝酸盐的0.9V(max)。溴酸盐，以及程度小得多的碘酸盐，也可作为替代底物。硝酸盐是氯酸盐还原的可逆竞争性抑制剂，这就解释了高浓度硝酸盐能部分逆转观察到的氯酸盐对细胞生长的抑制作用。在纯化的硝酸还原酶存在下，NADH还原氯酸盐的过程中，酶活性会逐渐发生不可逆抑制，推测这是由还原产物亚氯酸盐引起的。添加的亚氯酸盐使NADH-硝酸还原酶活性和相关的NADH-细胞色素c还原酶活性失活程度相同。与纯化酶相关的细胞色素b(557)的光谱特性不受亚氯酸盐影响。亚氯酸盐使硝酸还原酶失活可以解释氯酸盐对以硝酸盐为氮源生长的细胞的毒性，不过不能排除亚氯酸盐或其分解产物对其他细胞成分的破坏作用。
