Leclerc E, Leclerc L, Cassoly R, der Terrossian E, Wajcman H, Poyart C, Marden M C
INSERM U299, Hôpital de Bicêtre, France.
Arch Biochem Biophys. 1993 Oct;306(1):163-8. doi: 10.1006/abbi.1993.1495.
Heme-CO binds to the active (calcium-bound) form of calmodulin (CaM), but not to the inactive form. Despite a similarity in structure of another calcium-binding protein, skeletal muscle troponin C, both the affinity and the spectral red-shift of the absorption of the heme group are greatly decreased for troponin C relative to calmodulin. Parvalbumin, another calcium-binding protein, shows a twofold greater affinity for heme-CO relative to CaM. Unlike calmodulin and troponin C, the affinity of parvalbumin for heme-CO is even greater in the absence of calcium. The affinity of the tryptic and thrombic fragments of CaM for heme-CO are decreased relative to the entire calmodulin. The binding of heme-CO is specific as demonstrated by the discrimination of the calmodulin, troponin C, and parvalbumin pockets. The interaction of heme-CO with active (calcium-bound) CaM is rapid (ms) as determined by stopped flow measurements. No difference in kinetics was observed for mixing inactive (calcium free) CaM with a solution of [heme-CO plus calcium], indicating that the calcium-binding step and subsequent change in protein conformation are rapid.
血红素一氧化碳（Heme-CO）与钙调蛋白（CaM）的活性（结合钙的）形式结合，但不与非活性形式结合。尽管另一种钙结合蛋白——骨骼肌肌钙蛋白C在结构上有相似之处，但相对于钙调蛋白，肌钙蛋白C对血红素基团吸收的亲和力和光谱红移都大大降低。小清蛋白是另一种钙结合蛋白，它对血红素一氧化碳的亲和力是钙调蛋白的两倍。与钙调蛋白和肌钙蛋白C不同，小清蛋白在没有钙的情况下对血红素一氧化碳的亲和力甚至更高。相对于完整的钙调蛋白，钙调蛋白的胰蛋白酶和凝血酶片段对血红素一氧化碳的亲和力降低。如对钙调蛋白、肌钙蛋白C和小清蛋白口袋的区分所示，血红素一氧化碳的结合具有特异性。通过停流测量确定，血红素一氧化碳与活性（结合钙的）钙调蛋白的相互作用很快（毫秒级）。将非活性（无钙）钙调蛋白与[血红素一氧化碳加钙]溶液混合时，未观察到动力学差异，这表明钙结合步骤和随后的蛋白质构象变化很快。
