Geisow M J, Burgoyne R D
Nature. 1983 Feb 3;301(5899):432-5. doi: 10.1038/301432a0.
An increase in free calcium triggers catecholamine secretion from chromaffin cells and calmodulin is strongly implicated as the intracellular Ca2+ receptor. In our recent studies of calmodulin action in the chromaffin cell, micromolar Ca2+ concentrations resulted in calmodulin and cytosolic proteins becoming bound to the chromaffin granule membranes. We now report that calmodulin is bound with high affinity to granule membrane proteins of molecular weights (Mrs) 25,000 and 22,000 (25K and 22K) at low Ca2+ (less than 10(-8) M) and to proteins with Mrs 69K and 50K at high Ca2+ (greater than 1 microM). Other cytosolic components (Mrs 70K, 36K, 34K and 32K) require calmodulin for their interfraction with membrane. These proteins separately bound to calmodulin-Sepharose at high Ca2+ concentrations. Although the functions of these adrenal proteins have not been established, the 34K and 32K Mr components co-migrate with clathrin light chains isolated from medullary coated vesicles and the Mr 34K components from both sources share the same one-dimensional peptide map. These interactions were observed at micromolar Ca2+ levels at 'intracellular' conditions of pH and ionic strength and would be expected to occur during secretion from the chromaffin cell.
游离钙的增加会触发嗜铬细胞分泌儿茶酚胺，钙调蛋白被强烈认为是细胞内的钙离子受体。在我们最近对嗜铬细胞中钙调蛋白作用的研究中，微摩尔浓度的钙离子会导致钙调蛋白和胞质蛋白与嗜铬颗粒膜结合。我们现在报告，在低钙（小于10⁻⁸M）条件下，钙调蛋白以高亲和力与分子量为25000和22000（25K和22K）的颗粒膜蛋白结合，在高钙（大于1微摩尔）条件下与分子量为69K和50K的蛋白结合。其他胞质成分（分子量70K、36K、34K和32K）与膜的相互作用需要钙调蛋白。这些蛋白在高钙浓度下分别与钙调蛋白 - 琼脂糖结合。虽然这些肾上腺蛋白的功能尚未确定，但34K和32K分子量的成分与从髓质包被小泡中分离出的网格蛋白轻链共迁移，且来自这两个来源的34K分子量成分具有相同的一维肽图。在“细胞内”的pH和离子强度条件下，在微摩尔钙离子水平观察到了这些相互作用，预计在嗜铬细胞分泌过程中会发生。
