Orosz F, Vértessy B G, Hollán S, Horányi M, Ovádi J
Institute of Enzymology, Hungarian Academy of Sciences, Budapest, Hungary.
J Theor Biol. 1996 Oct 7;182(3):437-47. doi: 10.1006/jtbi.1996.0184.
Deficiencies in around 20 enzymes, associated with widely different degrees of severity and complexity, have been identified for human erythrocytes. The fact that glycolysis is crucial for erythrocyte function is reflected by the large number of inherited glycolytic enzymopathies. Triosephosphate isomerase (TPI) deficiency, a rare autosomal disease, is usually associated with nonspherocytic hemolytic anemia, progressive neurologic dysfunction, and death in childhood. The two affected Hungarian brothers studied by us have less than 3% TPI activity and enormously (30-50-fold) increased dihydroxyacetone phosphate (DHAP) concentration in their erythrocytes. The well-established concept of the metabolic control theory was used to test the contribution of TPI and some related enzymes to the control of a relevant segment of the glycolytic pathway in normal and deficient cells. Deviation indices, DEJ = (delta J/delta E) E(r)/J(r), which give a good estimation of flux control coefficients using a single large change in enzyme activity, were determined from the fluxes in the absence and presence of exogeneous enzymes. We found that PFK and aldolase are the enzymes that predominantly control the flux, however, the quantitative values depend extensively on the pH: DEJ values are 0.85 and 0.14 at pH 8.0 and 0.33 and 0.67 at pH 7.2 for aldolase and PFK, respectively. Neither the flux rates nor the capacities of the enzymes seem to be significantly different in normal and TPI deficient cells. There is a discrepancy between DHAP levels and TPI activities in the deficient cells. In contrast to the experimental data the theoretical calculations predict elevation in DHAP level at lower than 0.1% of the normal value of TPI activity. Several possibilities suggested fail to explain this discrepancy. Specific associations of glycolytic enzymes to band-3 membrane proteins with their concomitant inactivation have been demonstrated. We propose that the microcompartmentation of TPI that could further decrease the reduced isomerase activity of the deficient cells, is responsible for the high DHAP level.
已确定人类红细胞中约20种酶存在缺陷，这些缺陷与程度和复杂性差异很大的情况相关。大量遗传性糖酵解酶病反映了糖酵解对红细胞功能至关重要这一事实。磷酸丙糖异构酶（TPI）缺乏症是一种罕见的常染色体疾病，通常与非球形细胞溶血性贫血、进行性神经功能障碍以及儿童期死亡相关。我们研究的两名患病匈牙利兄弟红细胞中的TPI活性低于3%，而二羟基丙酮磷酸（DHAP）浓度大幅升高（30 - 50倍）。代谢控制理论中已确立的概念被用于测试TPI和一些相关酶对正常细胞和缺陷细胞中糖酵解途径相关部分控制的贡献。偏差指数DEJ = (δJ/δE)E(r)/J(r)，通过单一酶活性的大幅变化能很好地估算通量控制系数，它是根据有无外源酶时的通量来确定的。我们发现磷酸果糖激酶（PFK）和醛缩酶是主要控制通量的酶，然而，定量值在很大程度上取决于pH值：在pH 8.0时，醛缩酶和PFK的DEJ值分别为0.85和0.14，在pH 7.2时分别为0.33和0.67。正常细胞和TPI缺陷细胞中的通量速率和酶的能力似乎都没有显著差异。缺陷细胞中DHAP水平和TPI活性之间存在差异。与实验数据相反，理论计算预测在TPI活性低于正常值的0.1%时DHAP水平会升高。提出的几种可能性都无法解释这种差异。已证明糖酵解酶与带3膜蛋白存在特异性结合并伴随其失活。我们认为，TPI的微区室化可能进一步降低缺陷细胞中异构酶活性的降低，这是导致DHAP水平升高的原因。
