Conzelman K A, Mooseker M S
J Cell Biol. 1987 Jul;105(1):313-24. doi: 10.1083/jcb.105.1.313.
The microvillus 110-kD protein-calmodulin complex (designated 110K-CM) shares several properties with all myosins. In addition to its well-defined ATP-dependent binding interaction with F-actin, 110K-CM is an ATPase with diagnostically myosin-like divalent cation sensitivity. It exhibits maximum enzymatic activity in the presence of K+ and EDTA (0.24 mumol P1/mg per min) or in the presence of Ca++ (0.40 mumol P1/mg per min) and significantly less activity in physiological ionic conditions of salt and Mg++ (0.04 mumol P1/mg per min). This MgATPase is activated by F-actin in an actin concentration-dependent manner (up to 2.5-3.5-fold). The specific MgATPase activity of 110K-CM is also enhanced by the addition of 5-10 microM Ca++, but in the isolated complex, there is often also a decrease in the extent of actin activation in this range of free Ca++. Actin activation is maintained, however, in samples with exogenously added calmodulin; under these conditions, there is an approximately sevenfold stimulation of 110K-CM's enzymatic activity in the presence of 5-10 microM Ca++ and actin. 110K-CM is relatively indiscriminant in its nucleoside triphosphate specificity; in addition to ATP, GTP, CTP, UTP, and ITP are all hydrolyzed by the complex in the presence of either Mg++ or Ca++. Neither AMP nor the phosphatase substrate p-nitrophenyl phosphate are substrates for the enzymatic activity. The pH optimum for CaATPase activity is 6.0-7.5; maximum actin activation of MgATPase occurs over a broad pH range of 6.5-8.5. Finally, like myosins, purified 110K-CM crosslinks actin filaments into loosely ordered aggregates in the absence of ATP. Collectively these data support the proposal of Collins and Borysenko (1984, J. Biol. Chem., 259:14128-14135) that the 110K-CM complex is functionally analogous to the mechanoenzyme myosin.
微绒毛110-kD蛋白-钙调蛋白复合物（命名为110K-CM）与所有肌球蛋白具有若干共同特性。除了其与F-肌动蛋白明确的ATP依赖性结合相互作用外，110K-CM还是一种具有诊断性肌球蛋白样二价阳离子敏感性的ATP酶。在存在K⁺和EDTA（0.24 μmol P1/mg每分钟）时或在存在Ca²⁺（0.40 μmol P1/mg每分钟）时，它表现出最大酶活性，而在盐和Mg²⁺的生理离子条件下活性显著降低（0.04 μmol P1/mg每分钟）。这种MgATP酶被F-肌动蛋白以肌动蛋白浓度依赖性方式激活（高达2.5 - 3.5倍）。添加5 - 10 μM Ca²⁺也可增强110K-CM的比MgATP酶活性，但在分离的复合物中，在这个游离Ca²⁺范围内肌动蛋白激活程度通常也会降低。然而，在外源添加钙调蛋白的样品中肌动蛋白激活得以维持；在这些条件下，在存在5 - 10 μM Ca²⁺和肌动蛋白时，110K-CM的酶活性会受到约七倍的刺激。110K-CM在其三磷酸核苷特异性方面相对不具选择性；除了ATP外，GTP、CTP、UTP和ITP在存在Mg²⁺或Ca²⁺时都会被该复合物水解。AMP和磷酸酶底物对硝基苯磷酸都不是该酶活性的底物。CaATP酶活性的最适pH为6.0 - 7.5；MgATP酶的最大肌动蛋白激活发生在6.5 - 8.5的较宽pH范围内。最后，与肌球蛋白一样，纯化的110K-CM在不存在ATP的情况下将肌动蛋白丝交联成松散排列的聚集体。这些数据共同支持了Collins和Borysenko（1984年，《生物化学杂志》，259:14128 - 14135）的提议，即110K-CM复合物在功能上类似于机械酶肌球蛋白。
