Masaki R, Wada K, Matsubara H
J Biochem. 1977 Jan;81(1):1-9. doi: 10.1093/oxfordjournals.jbchem.a131423.
The acetylation of spinach ferredoxin by acetic anhydride modified about four moles of amino groups. The absorption spectra, CD spectra, the fluorescence of sole tryptophan residue and the biological activity of acetylated ferredoxin were investigated. An equilibrium existed between two different states, D- and N-form, of the acetylated ferredoxin and was dependent on the cation concentration. D-form completely reverted to N-form upon the binding of one mole of cation, Na+ or Mg2+. Although the N-form was indistinguishable from native ferredoxin in every property tested, the D-form was significantly different from the N-form or native ferredoxin and was very unstable, especially at low salt concentrations. It is suggested that the amino groups might be important in maintaining the protein conformation by forming salt linkages, but may not be essential for the activity. Furthermore, since the D-form, unlike the N-form and native ferredoxin, was inactive in the ferredoxin-NADP+ reductase [EC 1.6.7.1] assay system and had no inhibitory effect in this system, it was considered to be incapable of forming a complex with ferredoxin-NADP+ reductase. On the other hand, the N-form of the modified ferredoxin was as active as native ferredoxin. It is suggested that amino groups of spinach ferredoxin are not essential for the redox reaction of ferredoxin or for complex formation with the reductase.
菠菜铁氧化还原蛋白经乙酸酐乙酰化修饰后，约有四摩尔氨基被修饰。对乙酰化铁氧化还原蛋白的吸收光谱、圆二色光谱、唯一色氨酸残基的荧光以及生物活性进行了研究。乙酰化铁氧化还原蛋白的两种不同状态，即D型和N型之间存在平衡，且该平衡取决于阳离子浓度。一摩尔阳离子（Na⁺或Mg²⁺）结合后，D型会完全转变为N型。尽管在测试的各项性质中N型与天然铁氧化还原蛋白无法区分，但D型与N型或天然铁氧化还原蛋白有显著差异，且非常不稳定，尤其是在低盐浓度下。这表明氨基可能通过形成盐键对维持蛋白质构象很重要，但对活性可能并非必不可少。此外，由于D型与N型和天然铁氧化还原蛋白不同，在铁氧化还原蛋白 - NADP⁺还原酶[EC 1.6.7.1]测定系统中无活性且在该系统中无抑制作用，因此认为它无法与铁氧化还原蛋白 - NADP⁺还原酶形成复合物。另一方面，修饰后的铁氧化还原蛋白的N型与天然铁氧化还原蛋白活性相当。这表明菠菜铁氧化还原蛋白的氨基对于铁氧化还原蛋白的氧化还原反应或与还原酶形成复合物并非必不可少。
