Osborne H H, Hollaway M R
Biochem J. 1976 Jul 1;157(1):255-9. doi: 10.1042/bj1570255.
An investigation was made of the effect of NAD+ analogues on subunit interactions in yeast and rabbit muscle glyceraldehyde 3-phosphate dehydrogenases by using the subunit exchange (hybridization) method described previously [e.g. see Osborne & Hollaway (1975) Biochem. J. 151, 37-45]. The ligands ATP, ITP, ADP, AMP, cyclic AMP and ADP-ribose like NADH, all caused an apparent weakening of intramolecular subunit interactions, whereas NAD+ caused an apparent increase in the stability of the tetrameric enzyme molecules. A mixture of NMN and AMP, although it did not simulate completely the NAD+-induced 'tightening' of the enzyme structure, did result in a more than 20-fold decrease in the rate of subunit exchange compared with that in the presence of AMP alone. These results show that occupancy of the NMN subsite of the enzyme NAD+-binding site is insufficient in itself to give the marked tightening of the enzyme structure induced by NAD+. The 'tightening' effect is specific in that it seems to require a phosphodiester link between NMN and ADP-ribose. These effects are discussed in terms of the detailed X-ray structure of the lobster holoenzyme [Buehner et al. (1974) J. Mol. Biol. 90, 25-49].
采用先前描述的亚基交换（杂交）方法 [例如见奥斯本和霍拉韦（1975年），《生物化学杂志》151卷，37 - 45页]，研究了NAD⁺类似物对酵母和兔肌肉甘油醛-3-磷酸脱氢酶中亚基相互作用的影响。与NADH一样，配体ATP、ITP、ADP、AMP、环磷酸腺苷和ADP-核糖均导致分子内亚基相互作用明显减弱，而NAD⁺则导致四聚体酶分子稳定性明显增加。NMN和AMP的混合物虽然没有完全模拟出NAD⁺诱导的酶结构“收紧”，但与仅存在AMP时相比，确实使亚基交换速率降低了20多倍。这些结果表明，酶的NAD⁺结合位点的NMN亚位点被占据本身不足以产生由NAD⁺诱导的酶结构的显著收紧。“收紧”效应具有特异性，因为它似乎需要NMN和ADP-核糖之间存在磷酸二酯键。根据龙虾全酶的详细X射线结构 [比纳等人（1974年），《分子生物学杂志》90卷，25 - 49页] 对这些效应进行了讨论。
