Hitchcock S E
J Biol Chem. 1980 Jun 25;255(12):5668-73.
Deoxyribonuclease I (DNase I) forms a 1:1 complex with globular actin (G-actin) and also will depolymerize filamentous actin (F-actin) to form a 1:1 complex. The effect of DNase I on the exchange of the actin nucleotide has been investigated. When DNase I is added to G-actin, the rate of nucleotide exchange is decreased from 1.16 +/- 0.25 X 10(-4) s-1 to 0.28 +/- 0.09 X 10(-4) s-1 (0 degrees C). The presence of ATP or ADP in the actin has little effect on the rate of exchange of the nucleotide for ATP. This suggests that the weaker affinity of ADP than ATP for actin is due to a slower association rate of ADP. The rate of the nucleotide exchange in the actinDNase I complex is increased by the addition of NaCl or MgCl2. When DNase I is added to F-actin, the rate of nucleotide exchange (6.2 +/- 1.6 X 10(-4) x-1, 0 degrees C) is similar to the rate of depolymerization as measured by loss of viscosity. The actinDNase I complex formed by depolymerization of F-actin exchanges nucleotide at a 4-fold faster rate than the G-actinDNase I complex in the same ionic conditions. This and other experiments suggest that DNase I binds first to F-actin before dissociating the monomer from the filament. These results are discussed in terms of possible mechanisms of action depolymerization.
脱氧核糖核酸酶I（DNase I）与球状肌动蛋白（G-肌动蛋白）形成1:1复合物，并且还会使丝状肌动蛋白（F-肌动蛋白）解聚以形成1:1复合物。已经研究了DNase I对肌动蛋白核苷酸交换的影响。当将DNase I添加到G-肌动蛋白中时，核苷酸交换速率从1.16±0.25×10⁻⁴ s⁻¹降低到0.28±0.09×10⁻⁴ s⁻¹（0℃）。肌动蛋白中ATP或ADP的存在对核苷酸与ATP交换的速率影响很小。这表明ADP对肌动蛋白的亲和力比ATP弱是由于ADP的缔合速率较慢。通过添加NaCl或MgCl₂可提高肌动蛋白-DNase I复合物中核苷酸交换的速率。当将DNase I添加到F-肌动蛋白中时，核苷酸交换速率（6.2±1.6×10⁻⁴ s⁻¹，0℃）与通过粘度损失测量的解聚速率相似。由F-肌动蛋白解聚形成的肌动蛋白-DNase I复合物在相同离子条件下交换核苷酸的速率比G-肌动蛋白-DNase I复合物快4倍。这一结果和其他实验表明，DNase I在将单体从细丝上解离之前首先与F-肌动蛋白结合。将根据可能的解聚作用机制对这些结果进行讨论。
