Pick U, Bassilian S
Eur J Biochem. 1983 Jun 15;133(2):289-97. doi: 10.1111/j.1432-1033.1983.tb07461.x.
The effects of octylglucoside (OcGlc) micelles, which stimulate a Mg-specific ATPase activity in chloroplast coupling factor 1 [Pick, U. and Bassilian, S. (1982) Biochemistry, 21, 6144-6152], on the interactions of the enzyme with adenine nucleotides have been studied. 1. OcGlc specifically accelerates the binding and the release of ADP but not of ATP or adenosine 5'[beta, gamma-imido]triphosphate (AdoPP[NH]P) from the tight-sites. The binding affinity for ADP and for ATP is only slightly decreased (twofold) by the detergent. ATP competitively inhibits the binding of ADP and vice versa in the presence or absence of OcGlc. 2.OcGlc-induced inactivation of CF1-ATPase is correlated with the release of bound nucleotides. In the absence of medium nucleotides ADP X CF1 is rapidly inactivated while ATP X CF1 and AdoPP[NH]P X CF1 are slowly inactivated by OcGlc in parallel with the release of bound nucleotide. In contrast, low concentrations of either ATP or ADP in the medium effectively protect against OcGlc inactivation while AdoPP[NH]P, whose binding to CF1 is inhibited by OcGlc, is ineffective even at millimolar concentrations. The results suggest that the occupancy of the tight-sites protects the enzyme against OcGlc-induced inactivation. 3. Mg ions specifically inhibit the release of bound ADP and the OcGlc-induced inactivation of CF1. High concentrations of medium ATP and ADP (K50 = 100 microM) also inhibit the OcGlc-induced release of bound nucleotides in an EDTA medium. In contrast, in the absence of OcGlc, medium ADP and ATP accelerate the release of bound adenine nucleotides. 4. Mg-ATP in the presence of OcGlc stimulates the release of bound ADP from CF1. Bound ATP is neither released nor hydrolyzed at the tight-sites under these conditions where medium ATP is rapidly hydrolyzed. Mg-ADP stimulates the release of bound ADP only in the presence of inorganic phosphate or of phosphate analogs, e.g. arsenate, pyrophosphate or selenate. 5. It is suggested that: (a) ATP and ADP bind to the same tight-sites, but OcGlc activation specifically accelerates the exchange of bound ADP at the site. (b) CF1 contains low affinity adenine nucleotide binding sites which may be the catalytical sites and which influence the tight-sites by cooperative interactions. (c) Mg-ATP in the presence of OcGlc induces a conformational change at the catalytical site which accelerates the release of ADP from the tight-site. The implications of these results to the role of adenine nucleotides in the regulation and mechanism of ATP hydrolysis by CF1 are discussed.
已对辛基葡糖苷（OcGlc）胶束（其能刺激叶绿体偶联因子1中的Mg特异性ATP酶活性[皮克，U.和巴西利安，S.（1982年）《生物化学》，21卷，6144 - 6152页]）对该酶与腺嘌呤核苷酸相互作用的影响进行了研究。1. OcGlc特异性加速ADP从紧密位点的结合和释放，但不加速ATP或腺苷5'-[β，γ-亚氨基]三磷酸（AdoPP[NH]P）的结合和释放。去污剂仅使对ADP和ATP的结合亲和力略有降低（两倍）。在有或没有OcGlc的情况下，ATP竞争性抑制ADP的结合，反之亦然。2. OcGlc诱导的CF1-ATP酶失活与结合核苷酸的释放相关。在没有中等浓度核苷酸的情况下，ADP×CF1迅速失活，而ATP×CF1和AdoPP[NH]P×CF1被OcGlc缓慢失活，同时结合核苷酸释放。相反，培养基中低浓度的ATP或ADP有效防止OcGlc失活，而AdoPP[NH]P（其与CF1的结合被OcGlc抑制）即使在毫摩尔浓度下也无效。结果表明紧密位点的占据保护酶免受OcGlc诱导的失活。3. Mg离子特异性抑制结合ADP的释放和OcGlc诱导的CF1失活。高浓度的培养基ATP和ADP（K50 = 100 microM）在EDTA培养基中也抑制OcGlc诱导的结合核苷酸的释放。相反，在没有OcGlc的情况下，培养基中的ADP和ATP加速结合腺嘌呤核苷酸的释放。4. 在OcGlc存在下，Mg-ATP刺激CF1中结合ADP的释放。在这些条件下，中等浓度的ATP迅速水解，而结合的ATP既不释放也不在紧密位点水解。Mg-ADP仅在存在无机磷酸或磷酸类似物（如砷酸盐、焦磷酸盐或硒酸盐）时刺激结合ADP的释放。5. 有人提出：（a）ATP和ADP结合到相同的紧密位点，但OcGlc激活特异性加速该位点结合ADP的交换。（b）CF1含有低亲和力的腺嘌呤核苷酸结合位点，其可能是催化位点，并通过协同相互作用影响紧密位点。（c）在OcGlc存在下，Mg-ATP在催化位点诱导构象变化，加速ADP从紧密位点的释放。讨论了这些结果对腺嘌呤核苷酸在CF1催化ATP水解的调节和机制中的作用的影响。
