Valentine W N, Paglia D E, Nakatani M, Brockway R A
Department of Medicine, University of California, Los Angeles 90024.
Am J Hematol. 1987 Dec;26(4):353-6. doi: 10.1002/ajh.2830260408.
The half-saturation constant (K0.5s) phosphoenolpyruvate (PEP) for red cell pyruvate kinase (PK) with co-factors UDP and GDP is less than one-half that with ADP with or without additions of the allosteric modifier, fructose-1, 6-dephosphate (F-1, 6-P2) to the assay. The Vmax is markedly greater with ADP than with UDP or GDP, but with (PEP) at 0.5 mM, activity with all co-factors is about equal and at lower concentrations greater with UDP and GDP. With high K0.5s (PEP) mutant enzymes, and at the usual test concentration (lmM) for PEP when nucleotide specificity is assessed, the abnormally low saturation of variant enzymes may result in higher activity with UDP and GDP than with ADP--the opposite of the "normal situation." The apparent aberration in nucleotide specificity may thus be illusory and secondary to the abnormal K0.5s (PEP) of the mutant. Example data are recorded. Variations in K0.5s (PEP) may also be introduced during enzyme preparation for assay, particularly when partial purification is employed.
红细胞丙酮酸激酶（PK）在有辅因子UDP和GDP存在时，磷酸烯醇丙酮酸（PEP）的半饱和常数（K0.5s）小于有或无变构调节剂1,6-二磷酸果糖（F-1,6-P2）添加到测定体系时与ADP存在时的一半。Vmax在有ADP时明显大于有UDP或GDP时，但在PEP浓度为0.5 mM时，所有辅因子存在时的活性大致相等，在较低浓度时，UDP和GDP存在时的活性更高。对于具有高K0.5s（PEP）的突变酶，以及在评估核苷酸特异性时PEP的常用测试浓度（1 mM）下，变异酶异常低的饱和度可能导致与UDP和GDP相比，ADP存在时活性更高——这与“正常情况”相反。因此，核苷酸特异性的明显异常可能是虚幻的，并且是突变体异常的K0.5s（PEP）的继发结果。记录了示例数据。在用于测定的酶制备过程中，尤其是采用部分纯化时，K0.5s（PEP）也可能发生变化。
