Kahane I, Ne'eman Z, Razin S
J Bacteriol. 1973 Feb;113(2):666-71. doi: 10.1128/jb.113.2.666-671.1973.
The Mg(2+) content of membranes of several Mycoplasma and Acholeplasma species varied between 0.88 and 1.98 mug of Mg(2+) per mg of protein, depending on the species and on growth conditions. Ca(2+) could be detected only when it was added to the growth medium. The Mg(2+) content of isolated A. laidlawii membranes could be increased almost threefold by dialysis against 20 mm Mg(2+), whereas aggregated A. laidlawii membranes contained about six to eight times more Mg(2+) per mg of protein than the native membranes. This was taken to indicate that the molecular organization of the lipid and protein in the reaggregated membranes differs from that of the native membranes. Between 60 and 83% of the Mg(2+) in native and reaggregated A. laidlawii membranes was associated with the lipid fraction extracted with chloroform-methanol. The removal of over 80% of membrane protein by Pronase digestion did not release any significant amount of Mg(2+). Hence, most of the divalent cation appears to be bound to membrane lipids, most probably to phospholipids. Ethylenediaminetetraacetic acid released the bulk of Mg(2+) bound to the native and reaggregated A. laidlawii membranes, except for about 0.5 mug of Mg(2+) per mg of protein which was too tightly bound. Hence, a small but fairly constant amount of Mg(2+) is unavailable for chelation.
几种支原体和无胆甾原体细胞膜中的镁离子（Mg²⁺）含量在每毫克蛋白质含0.88至1.98微克Mg²⁺之间，具体取决于物种和生长条件。只有当向生长培养基中添加钙离子（Ca²⁺）时才能检测到它。通过用20 mM Mg²⁺进行透析，分离的莱氏无胆甾原体细胞膜中的Mg²⁺含量可增加近三倍，而聚集的莱氏无胆甾原体细胞膜每毫克蛋白质所含的Mg²⁺比天然细胞膜多约六至八倍。这表明重新聚集的细胞膜中脂质和蛋白质的分子组织与天然细胞膜不同。天然和重新聚集的莱氏无胆甾原体细胞膜中60%至83%的Mg²⁺与用氯仿 - 甲醇提取的脂质部分相关。用链霉蛋白酶消化去除超过80%的膜蛋白并没有释放出任何大量的Mg²⁺。因此，大多数二价阳离子似乎与膜脂质结合，很可能是与磷脂结合。乙二胺四乙酸（EDTA）释放了与天然和重新聚集的莱氏无胆甾原体细胞膜结合的大部分Mg²⁺，除了每毫克蛋白质约0.5微克的Mg²⁺结合过于紧密。因此，有少量但相当恒定的Mg²⁺无法用于螯合。
