Thuillier L
Biochim Biophys Acta. 1978 May 11;524(1):198-206. doi: 10.1016/0005-2744(78)90118-3.
Inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1) from human erythrocyte hemolysates has been purified up to 10 000-fold. The purified enzyme is homogenous and has a specific activity of 79.75 mumol PPi hydrolysed.min-1.mg-1 at pH 8 and 37 degrees C. It was confirmed that it is a dimer with a molecular weight of 42 000, composed of two identical protomers. From kinetic studies, it is proposed that human erythrocyte inorganic pyrophosphatase activity depends on free Mg2+ concentration in different ways. This ion constitutes part of the substrate (the Mg.PPi complex; Km = 1.4.10(-4) M) and probably acts as an allosteric activator (kinetic activation constant: KMg2+a = 7.5.10(-4) M). Equilibrium binding studies performed in the absence of PPi showed 4 binding sites for Mg2+, all having the same high affinity (dissociation constant: KMg2+d = 4.10(-6) M). Since the concentration of free Mg2+ in red blood cells is very low and may vary with the oxygenation state, it is likely that in vivo erythrocyte pyrophosphatase activity is regulated.
人红细胞溶血产物中的无机焦磷酸酶（焦磷酸磷酸水解酶，EC 3.6.1.1）已被纯化至10000倍。纯化后的酶是均一的，在pH 8和37℃时比活性为79.75 μmol PPi水解·min⁻¹·mg⁻¹。已证实它是一种二聚体，分子量为42000，由两个相同的亚基组成。通过动力学研究表明，人红细胞无机焦磷酸酶的活性以不同方式依赖于游离Mg²⁺浓度。该离子构成底物的一部分（Mg·PPi复合物；Km = 1.4×10⁻⁴ M），并且可能作为变构激活剂（动力学激活常数：KMg²⁺a = 7.5×10⁻⁴ M）。在不存在PPi的情况下进行的平衡结合研究显示，Mg²⁺有4个结合位点，所有位点都具有相同的高亲和力（解离常数：KMg²⁺d = 4×10⁻⁶ M）。由于红细胞中游离Mg²⁺的浓度非常低，并且可能随氧合状态而变化，因此体内红细胞焦磷酸酶的活性很可能受到调节。
