Valiyaveetil Francis, Hermolin Joe, Fillingame Robert H
Department of Biomolecular Chemistry, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, USA.
Biochim Biophys Acta. 2002 Feb 15;1553(3):296-301. doi: 10.1016/s0005-2728(01)00251-1.
The pH dependence of the reaction of dicyclohexylcarbodiimide with the essential aspartyl-61 residue in subunit c of Escherichia coli ATP synthase was compared in membranes and in a detergent dispersed preparation of the enzyme. The rate of reaction was estimated by measuring the inactivation of ATPase activity. The reaction with the detergent dispersed form of the enzyme proved to be pH sensitive with the essential aspartyl group titrating with a pK(a)=8. However, when measured with E. coli membranes, the reaction proved to be pH insensitive. The results suggest that the reacting aspartyl-61 residues are shielded from the bulk aqueous solvent when in the membrane, but then become aqueous-accessible following detergent solubilization.
在大肠杆菌ATP合酶亚基c中，二环己基碳二亚胺与必需的天冬氨酸61残基反应的pH依赖性，在膜中和在去污剂分散的酶制剂中进行了比较。通过测量ATP酶活性的失活来估计反应速率。事实证明，与去污剂分散形式的酶的反应对pH敏感，必需的天冬氨酸基团的滴定pK(a)=8。然而，当用大肠杆菌膜进行测量时，反应证明对pH不敏感。结果表明，反应性天冬氨酸61残基在膜中时被与大量水相溶剂隔离，但在去污剂增溶后变得可与水接触。
