Wu W, Berkowitz G A
Horticulture Department, Cook College, Rutgers-The State University of New Jersey, New Brunswick, New Jersey 08903.
Plant Physiol. 1992 Jun;99(2):553-60. doi: 10.1104/pp.99.2.553.
Studies were conducted to characterize ATPase activity associated with purified chloroplast inner envelope preparations from spinach (Spinacea oleracea L.) plants. Comparison of free Mg(2+) and Mg.ATP complex effects on ATPase activity revealed that any Mg(2+) stimulation of activity was likely a function of the use of the Mg.ATP complex as a substrate by the enzyme; free Mg(2+) may be inhibitory. In contrast, a marked (one- to twofold) stimulation of ATPase activity was noted in the presence of K(+). This stimulation had a pH optimum of approximately pH 8.0, the same pH optimum found for enzyme activity in the absence of K(+). K(+) stimulation of enzyme activity did not follow simple Michaelis-Menton kinetics. Rather, K(+) effects were consistent with a negative cooperativity-type binding of the cation to the enzyme, with the K(m) increasing at increasing substrate. Of the total ATPase activity associated with the chloroplast inner envelope, the K(+)-stimulated component was most sensitive to the inhibitors oligomycin and vanadate. It was concluded that K(+) effects on this chloroplast envelope ATPase were similar to this cation's effects on other transport ATPases (such as the plasmalemma H(+)-ATPase). Such ATPases are thought to be indirectly involved in active K(+) uptake, which can be facilitated by ATPase-dependent generation of an electrical driving force. Thus, K(+) effects on the chloroplast enzyme in vitro were found to be consistent with the hypothesized role of this envelope ATPase in facilitating active cation transport in vivo.
开展了多项研究，以表征与菠菜（Spinacea oleracea L.）植株纯化的叶绿体内膜制剂相关的ATP酶活性。比较游离Mg(2+)和Mg·ATP复合物对ATP酶活性的影响发现，Mg(2+)对活性的任何刺激可能是该酶将Mg·ATP复合物用作底物的结果；游离Mg(2+)可能具有抑制作用。相比之下，在存在K(+)的情况下，ATP酶活性有显著（1至2倍）的刺激。这种刺激的最适pH约为8.0，与不存在K(+)时酶活性的最适pH相同。K(+)对酶活性的刺激不遵循简单的米氏动力学。相反，K(+)的作用与阳离子与酶的负协同型结合一致，随着底物增加，K(m)增大。在与叶绿体内膜相关的总ATP酶活性中，K(+)刺激的组分对抑制剂寡霉素和钒酸盐最为敏感。得出的结论是，K(+)对这种叶绿体膜ATP酶的作用类似于该阳离子对其他转运ATP酶（如质膜H(+)-ATP酶）的作用。这种ATP酶被认为间接参与主动K(+)吸收，而ATP酶依赖性产生的电驱动力可促进这种吸收。因此，发现K(+)在体外对叶绿体酶的作用与该膜ATP酶在体内促进阳离子主动转运的假设作用一致。
