CORRELATION PROTON MAGNETIC-RESONANCE STUDIES AT 250-MHZ OF BOVINE PANCREATIC RIBONUCLEASE .2. PH AND INHIBITOR-INDUCED CONFORMATIONAL TRANSITIONS AFFECTING HISTIDINE-48 AND ONE TYROSINE RESIDUE OF RIBONUCLEASE-A
CORRELATION PROTON MAGNETIC-RESONANCE STUDIES AT 250-MHZ OF BOVINE PANCREATIC RIBONUCLEASE .2. PH AND INHIBITOR-INDUCED CONFORMATIONAL TRANSITIONS AFFECTING HISTIDINE-48 AND ONE TYROSINE RESIDUE OF RIBONUCLEASE-A
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DOI：
10.1021/bi00687a007
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发表时间：
1975-01-01
期刊：
影响因子：
2.9
通讯作者：
MARKLEY, JL
中科院分区：
文献类型：
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作者：
MARKLEY, JL
为了简化组氨酸-48的C(2)-H共振谱的拆分，用质子核磁共振技术研究了牛胰腺核糖核酸酶A的组氨酸-48的微环境。核糖核酸A的组氨酸-48在100 MHz和250 MHz处的核磁共振滴定曲线是不连续的，无论是该酶在0.3M的氯化物中，还是它与胞苷3‘-磷酸的络合物。这表明，组氨酸-48的滴定只发生在缓慢的构象转变的结果。在该酶的酸稳定和碱稳定形式中，对应于组氨酸-48的峰的总和不到一个质子，这表明该酶至少存在一种中间构象。由酸稳定型向中间型转变的PHm‘d为5.6，从中间型向碱稳定型转变的PHMid为6.9。在核糖核酸酶S和0.3M醋酸盐存在下的核糖核酸酶A中，组氨酸-48的滴定曲线是连续的，峰面积在整个滴定过程中是均匀的。
The microenvironment of histidine-48 of bovine pancreatic ribonuclease A was investigated by proton magnetic resonance spectroscopy (NMR) using partial-ly deuterated enzyme in which resolution of the C (2)-H resonance of histidine-48 was simplified. The NMR titra-tion curves at 100 and 250 MHz of histidine-48 of ribonu-clease A are discontinuous both for the enzyme alone in 0.3 M chloride and for its complex with cytidine 3'-phosphate. This suggests that titration of histidine-48 occurs only as the result of a slow conformational transition. The sum of the peaks corresponding to histidine-48 in the acid-stable and base-stable forms of the enzyme isless than one proton in the transition region, which indicates that there exists at least one intermediate conformational formof the enzyme. The transition from the acid-stable form to an intermediate form has a pHm¡ d of 5.6, and the transition from an intermediate form to the base-stable form has a pHmid of 6.9. In ribonuclease S and in ribonuclease A in the presence of 0.3 M acetate, the titration curve of histidine-48 is continuous, and the area of the peak is uniform throughout the titration.