Fleischman D, Denisevich M
Biochemistry. 1979 Nov 13;18(23):5060-6. doi: 10.1021/bi00590a006.
The guanylate cyclase activity of axoneme--basal apparatus complexes isolated from bovine retinal rods has been investigated. The Mg2+ and Mn2+ complexes of GTP4- serve as substrates. Binding of an additional mole of Mg2+ or Mn2+ per mole of enzyme is required. Among cations which are ineffective are Ca2+, Ni2+, Fe2+, Fe3+, Zn2+, and Co2+. The kinetics are consistent with a mechanism in which binding of Mg2+ or Mn2+ to the enzyme must precede binding of MgGTP or MnGTP. The apparent dissociation constants of the Mg--enzyme complex and the Mn--enzyme complex are 9.5 x 10(-4) and 1.1 x 10(-4) M, respectively. The apparent dissociation constants for binding of MgGTP and MnGTP to the complex of the enzyme with the same metal are 7.9 x 10(-4) and 1.4 x 10(-4) M, respectively. The cyclase activity is maximal and independent of pH between pH 7 and 9. KCl and NaCl are stimulatory, especially at suboptimal concentrations of Mg2+ or Mn2+. Ca2+ and high concentrations of Mg2+ and Mn2+ are inhibitory. Ca2+ inhibition appears to require the binding of 2 mol of Ca2+ per mol of enzyme. The dissociation constant of the Ca2--enzyme complex is estimated to be 1.4 x 10(-6) M2. The axoneme--basal apparatus preparations contain adenylate cyclase activity whose magnitude is 1--10% that of the guanylate cyclase activity.
对从牛视网膜杆状细胞中分离出的轴丝-基体复合物的鸟苷酸环化酶活性进行了研究。GTP4-的Mg2+和Mn2+复合物可作为底物。每摩尔酶需要额外结合一摩尔的Mg2+或Mn2+。无效的阳离子包括Ca2+、Ni2+、Fe2+、Fe3+、Zn2+和Co2+。动力学符合一种机制，即Mg2+或Mn2+与酶的结合必须先于MgGTP或MnGTP的结合。Mg-酶复合物和Mn-酶复合物的表观解离常数分别为9.5×10(-4)和1.1×10(-4)M。MgGTP和MnGTP与同一金属的酶复合物结合的表观解离常数分别为7.9×10(-4)和1.4×10(-4)M。环化酶活性在pH 7至9之间最大且与pH无关。KCl和NaCl具有刺激作用，尤其是在Mg2+或Mn2+浓度低于最佳浓度时。Ca2+以及高浓度的Mg2+和Mn2+具有抑制作用。Ca2+抑制似乎需要每摩尔酶结合2摩尔的Ca2+。Ca2-酶复合物的解离常数估计为1.4×10(-6)M2。轴丝-基体制剂含有腺苷酸环化酶活性，其活性大小为鸟苷酸环化酶活性的1-10%。
