Hasselbach W, Stephan L
Z Naturforsch C J Biosci. 1987 May;42(5):641-52.
The effect of hydrostatic pressure on calcium dependent p-nitrophenyl phosphate hydrolysis of the sarcoplasmic reticulum calcium transport enzyme has been investigated at different degree of enzyme saturation by calcium and Mg-p-nitrophenyl phosphate to distinguish between activation and binding volumes. The enzyme saturated by both ligands displays a significant dependence of the activation volume on pressure, rising from 20 ml/mol at atmospheric pressure (0.1 MPa) to 80 ml/mol at 100 MPa. At subsaturating concentration of Mg-p-nitrophenyl phosphate an activation volume of 35 ml/mol prevails between 0.1 and 40 MPa. At subsaturating concentration of calcium the activation volume approximates 80 ml/mol in the same pressure range. The binding volume for both substrates is likewise pressure dependent falling from 20 ml/mol to 0 ml/mol for Mg-p-nitrophenyl phosphate and rising from 67 ml/mol to 155 ml/mol for calcium. The pressure dependence of activation and binding volumes is analysed on account of a simplified reaction scheme yielding activation volumes and rate constants for individual reaction steps.
在肌浆网钙转运酶被钙和对硝基苯磷酸镁不同程度饱和的情况下，研究了流体静压对其钙依赖性对硝基苯磷酸水解的影响，以区分活化体积和结合体积。被两种配体饱和的酶显示出活化体积对压力有显著依赖性，从常压（0.1MPa）下的20ml/mol上升到100MPa下的80ml/mol。在对硝基苯磷酸镁亚饱和浓度下，在0.1至40MPa之间，活化体积普遍为35ml/mol。在钙亚饱和浓度下，在相同压力范围内，活化体积约为80ml/mol。两种底物的结合体积同样依赖于压力，对硝基苯磷酸镁的结合体积从20ml/mol降至0ml/mol，钙的结合体积从67ml/mol升至155ml/mol。基于一个简化的反应方案分析了活化体积和结合体积的压力依赖性，该方案给出了各个反应步骤的活化体积和速率常数。
