Briley P A, Eisenthal R, Harrison R, Smith G D
Biochem J. 1977 May 1;163(2):325-31. doi: 10.1042/bj1630325.
Difluoro-oxaloacetate interacts with the aldimine form of aspartate transaminase to give a complex, the dissociation constant of which has been determined spectrophotometrically and by 19F n.m.r. (nuclear magnetic resonance). The 19F n.m.r. line-width-pH and chemical-shift-pH profiles of difluoro-oxaloacetate in the presence of the aldimine form of the enzyme both show inflexion points in the pH5 and pH8 regions, which may arise from variations in the binding of difluoro-oxaloacetate as specific groups on the enzyme are successively protonated. Difluoro-oxaloacetate also interacts with apoenzyme to form a complex, the dissociation constant of which was determined by 19F n.m.r. The 19F n.m.r. line-width-pH and chemical-shift-pH profiles of difluoro-oxaloacetate in the presence of apoenzyme show a single inflexion point in the region of pH8. The absence, in this case, of an inflexion in the pH5 region indicates that the latter, present in the corresponding profiles for the aldimine form of the enzyme, results from ionization of an enzyme group associated with the pyridoxal phosphate cofactor.
二氟草酰乙酸与天冬氨酸转氨酶的醛亚胺形式相互作用形成一种复合物，其解离常数已通过分光光度法和19F核磁共振法测定。在酶的醛亚胺形式存在下，二氟草酰乙酸的19F核磁共振线宽-pH和化学位移-pH曲线在pH5和pH8区域均显示拐点，这可能是由于随着酶上特定基团相继质子化，二氟草酰乙酸的结合发生变化所致。二氟草酰乙酸还与脱辅基酶相互作用形成一种复合物，其解离常数通过19F核磁共振法测定。在脱辅基酶存在下，二氟草酰乙酸的19F核磁共振线宽-pH和化学位移-pH曲线在pH8区域显示一个单一的拐点。在这种情况下，pH5区域没有拐点表明，在酶的醛亚胺形式的相应曲线中出现的后者是由与磷酸吡哆醛辅因子相关的酶基团的电离引起的。
