Ngai P K, Walsh M P
Biochem J. 1985 Sep 15;230(3):695-707. doi: 10.1042/bj2300695.
Chicken gizzard smooth muscle contains two major calmodulin-binding proteins: caldesmon (11.1 microM; Mr 141 000) and myosin light-chain kinase (4.6 microM; Mr 136 000), both of which are associated with the contractile apparatus. The amino acid composition of caldesmon is distinct from that of myosin light-chain kinase and is characterized by a very high glutamic acid content (25.5%), high contents of lysine (13.6%) and arginine (10.3%), and a low aromatic amino acid content (2.4%). Caldesmon lacked myosin light-chain kinase and phosphatase activities and did not compete with either myosin light-chain kinase or cyclic nucleotide phosphodiesterase (both calmodulin-dependent enzymes) for available calmodulin, suggesting that calmodulin may have distinct binding sites for caldesmon on the one hand and myosin light-chain kinase and cyclic nucleotide phosphodiesterase on the other. Consistent with the lack of effect of caldesmon on myosin phosphorylation, caldesmon did not affect the assembly or disassembly of myosin filaments in vitro. As previously shown [Ngai & Walsh (1984) J. Biol. Chem. 259, 13656-13659], caldesmon can be reversibly phosphorylated. The phosphorylation and dephosphorylation of caldesmon were further characterized and the Ca2+/calmodulin-dependent caldesmon kinase was purified; kinase activity correlated with a protein of subunit Mr 93 000. Caldesmon was not a substrate of myosin light-chain kinase or phosphorylase kinase, both calmodulin-activated protein kinases.
钙调素（11.1微摩尔；分子量141000）和肌球蛋白轻链激酶（4.6微摩尔；分子量136000），二者均与收缩装置相关。钙调素的氨基酸组成不同于肌球蛋白轻链激酶，其特点是谷氨酸含量非常高（25.5%），赖氨酸（13.6%）和精氨酸（10.3%）含量高，而芳香族氨基酸含量低（2.4%）。钙调素缺乏肌球蛋白轻链激酶和磷酸酶活性，并且在可利用的钙调蛋白方面，它不与肌球蛋白轻链激酶或环核苷酸磷酸二酯酶（二者均为钙调蛋白依赖性酶）竞争，这表明钙调蛋白一方面可能对钙调素具有不同的结合位点，另一方面对肌球蛋白轻链激酶和环核苷酸磷酸二酯酶具有不同的结合位点。与钙调素对肌球蛋白磷酸化缺乏影响一致，钙调素在体外不影响肌球蛋白丝的组装或拆卸。如先前所示[Ngai和Walsh（1984年）《生物化学杂志》259，13656 - 13659]，钙调素可以被可逆地磷酸化。对钙调素的磷酸化和去磷酸化进行了进一步表征，并纯化了Ca2 + /钙调蛋白依赖性钙调素激酶；激酶活性与亚基分子量93000的一种蛋白质相关。钙调素不是肌球蛋白轻链激酶或磷酸化酶激酶（二者均为钙调蛋白激活的蛋白激酶）的底物。
