Müller K, Garel J R
Biochemistry. 1984 Feb 14;23(4):651-4. doi: 10.1021/bi00299a010.
In the range of guanidine hydrochloride concentrations from 0.2 to 1.2 M, aspartokinase-homoserine dehydrogenase I loses its enzymatic properties, both kinase and dehydrogenase activities and their allosteric inhibition by L-threonine. Ligands which stabilize the tetrameric native structure protect the enzyme against inactivation. Under some conditions, all the functional properties do not disappear at the same rate: an intermediate species possessing only the kinase activity can be detected. Several arguments suggest that this partly active intermediate has a monomeric structure. These results show that deactivation of aspartokinase-homoserine dehydrogenase I is a stepwise process, compatible with the reverse of the previously described reactivation [Garel, J.-R., & Dautry-Varsat, A. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 3379-3383]. The same measurements performed with a monofunctional fragment carrying the dehydrogenase activity show that the loss of dehydrogenase activity is the same whether or not the polypeptide chain is intact or lacks the kinase region; this finding suggests that the protein is composed of independent regions. The influence of protein aggregation in studying unfolding-refolding of oligomeric enzymes is also discussed.
在盐酸胍浓度为0.2至1.2 M的范围内，天冬氨酸激酶-高丝氨酸脱氢酶I失去其酶活性，包括激酶和脱氢酶活性以及它们受L-苏氨酸的变构抑制作用。稳定四聚体天然结构的配体可保护该酶不被失活。在某些条件下，所有功能特性并非以相同速率消失：可以检测到仅具有激酶活性的中间物种。有几个论据表明这种部分活性中间体具有单体结构。这些结果表明，天冬氨酸激酶-高丝氨酸脱氢酶I的失活是一个逐步过程，这与之前描述的再激活过程相反[加雷尔，J.-R.，& 多特里-瓦尔萨特，A.（1980年）《美国国家科学院院刊》77，3379 - 3383]。对携带脱氢酶活性的单功能片段进行的相同测量表明，无论多肽链是完整的还是缺少激酶区域，脱氢酶活性的丧失情况是相同的；这一发现表明该蛋白质由独立区域组成。还讨论了蛋白质聚集在寡聚酶展开-重折叠研究中的影响。
