Brandts J F, Taverna R D, Sadasivan E, Lysko K A
Biochim Biophys Acta. 1978 Oct 4;512(3):566-78. doi: 10.1016/0005-2736(78)90166-9.
Differential scanning calorimetry has been used to study several structural transitions of the human erythrocyte membrane. Earlier studies have shown that one of these transitions (the A transition) is due to the thermal unfolding of spectrin on the membrane. In this paper, it is shown that two of the other transitions (B and C) exhibit a high sensitivity to a local anesthetic, benzyl alcohol. Increasing the ionic strength of the suspending medium results in a splitting of the B transition into two indepent transitions (B1 and B2). It is found that one of these (B2) is associated with titrating groups, since the midpoint for the transitions shifts by about 20 degrees C, with an apparent pK near 7.5 Extensive bilateral proteolysis by papain causes a drastic decrease in the size of all transitions except the C transition, which remains unaltered. On the other hand, treatment with phospholipase by A2 largely affects the C transition, causing its disappearance. Because of the lack of sensitivity to proteolysis and the high sensitivity to phospholipase, it appears that the C transition has a large extent of 'lipid involvement'. It might result from the melting of a small fraction of phospholipid which exists in a crystalline state under physiological conditions. Alternatively, the C transition could arise from changes in protein-lipid interactions or from lipid-dependent changes in protein-protein interactions, providing one assumes that only protease-resistant portions of membrane proteins are participating.
差示扫描量热法已被用于研究人红细胞膜的几种结构转变。早期研究表明，其中一种转变（A转变）是由于膜上血影蛋白的热解折叠所致。本文表明，其他两种转变（B和C）对局部麻醉剂苄醇表现出高度敏感性。增加悬浮介质的离子强度会导致B转变分裂为两个独立的转变（B1和B2）。发现其中之一（B2）与滴定基团有关，因为转变的中点移动了约20℃，表观pK接近7.5。木瓜蛋白酶广泛的双侧蛋白水解导致除C转变外所有转变的大小急剧减小，而C转变保持不变。另一方面，用磷脂酶A2处理在很大程度上影响C转变，导致其消失。由于对蛋白水解不敏感且对磷脂酶高度敏感，似乎C转变在很大程度上涉及“脂质”。它可能是由一小部分在生理条件下呈结晶态的磷脂的熔化引起的。或者，C转变可能源于蛋白质-脂质相互作用的变化或蛋白质-蛋白质相互作用中脂质依赖性的变化，前提是假定只有膜蛋白中抗蛋白酶的部分参与其中。
