Müller E, Hegewald H, Klinger R, Wetzker R, Cumme G A, Frunder H
Institute of Biochemistry II, Medical Faculty, Friedrich Schiller University, Jena, Germany.
Biol Chem. 1996 Dec;377(12):851-6.
Effects of intracellular pH and Mg2+ on turnover and extent of metabolic compartmentation of phosphomonoester groups of phosphoinositides and phosphatidate were investigated in human erythrocytes by short-term and equilibrium labeling with [32P]Pi under steady-state conditions. At pH 6.7, the specific radio-activities of phosphoinositides reached apparent equilibrium values, in the range of 70% of that ATP-gamma-P after long-term labelling. At pH 7.2, these values were in the range of 40-50% of that ATP-gamma-P. This demonstrates a decreased accessibility of phosphoinositides to enzymatic phosphorylation and dephosphorylation at the transition from acidic to normal incubation conditions. These changes were more pronounced at pH 7.8. High intracellular [Mg2+] initially activated the turnover of phosphoinositides at pH 7.2. The activation changed into an inhibition and an increase of metabolic compartmentation after three hours preincubation of erythrocytes at high [Mg2+]. The long-term Mg2+ effects are reversible to a great extent by a subsequent re-reduction of [Mg2+]. In conclusion, deprotonation of phosphoinositides by low [H+] or high intracellular [Mg2+] at normal pH induces a decreased accessibility for their specific lipid kinases and phosphatases. This effect may be the result of lateral phase separation of acidic phospholipids as a consequence of divalent cation complexation under both experimental conditions, high pH and high [Mg2+] at normal pH.
在稳态条件下，通过用[32P]Pi进行短期和平衡标记，研究了细胞内pH值和Mg2+对人红细胞中磷酸肌醇和磷脂酸磷酸单酯基团的周转及代谢区室化程度的影响。在pH 6.7时，磷酸肌醇的比放射性达到明显的平衡值，在长期标记后为ATP-γ-P的70%左右。在pH 7.2时，这些值在ATP-γ-P的40%-50%范围内。这表明在从酸性孵育条件转变为正常条件时，磷酸肌醇对酶促磷酸化和去磷酸化的可及性降低。这些变化在pH 7.8时更为明显。高细胞内[Mg2+]最初在pH 7.2时激活了磷酸肌醇的周转。在高[Mg2+]下对红细胞进行三小时预孵育后，这种激活转变为抑制和代谢区室化增加。长期的Mg2+效应在很大程度上可通过随后[Mg2+]的再次降低而逆转。总之，在正常pH下，低[H+]或高细胞内[Mg2+]导致的磷酸肌醇去质子化会使其特异性脂质激酶和磷酸酶的可及性降低。这种效应可能是在高pH和正常pH下高[Mg2+]这两种实验条件下，由于二价阳离子络合导致酸性磷脂横向相分离的结果。
