Kimura H, Mittal C K, Murad F
J Biol Chem. 1976 Dec 25;251(24):7769-73.
Native soluble and particulate guanylate cyclase from several rat tissues preferred Mn2+ to Mg2+ as the sole cation cofactor. Wtih 4mM cation, activities with Mg2+ were less than 25% of the activities with Mn2+. The 1 mM NaN3 markedly increased the activity of soluble and particulate preparations from rat liver. Wtih NaN3 activation guanylate cyclase activities wite similar with Mn2+ and Mg2+. Co2+ was partially effective as a cofactor in the presence of NaN3, while Ca2+ was a poor cation with or without NaN3. Activities with Ba, Cu2+, or Zn2+ were not detectable without or with 1 mM NaN3. With soluble liver enzyme both manganese and magnesium activities were dependent upon excess Mn2+ or Mg2+ at a fixed MnGTP or MgGTP concentration of 0.4 mm; apparent Km values for excess Mn2+ and Mg2+ were 0.3 and 0.24 mM, respectively. After NaN3 activation, the activity was less dependent upon free Mn2+ and retained its dependence for free Mg2+, at 0.4 mM MgGTP the apparent Km for excess Mg2+ was 0.3 mM. The activity of soluble liver guanylate cyclase assayed with Mn2+ or Mg2+ was increased with Ca2+. After NaN3 activiation, Ca2+ had no effect or was somewhat inhibitory with either Mn2+. After NaN activation, Ca2+ had no effect or was somewhat inhibitory with either Mn2+ or Mg2+. The stimulatory effect of NaN2 on Mn2+-and Mg2+-dependent guanylate cyclase activity from liver or cerebral cortex supernatant fractions required the presence of the sodium azide-activator factor. With partially purified soluble liver guanylate cyclase and azide-activator factor, the concentration (1 mjM) of NaN3 that gave half-maximal activation with Mn2+ or Mg2+ was imilar. Thus, under some conditions guanylate cyclase can effectively use Mg2+ as a sole cation cofactor.
来自几种大鼠组织的天然可溶性和颗粒性鸟苷酸环化酶更倾向于以Mn2+而非Mg2+作为唯一的阳离子辅因子。在阳离子浓度为4 mM时，以Mg2+存在时的活性不到以Mn2+存在时活性的25%。1 mM的NaN3显著提高了大鼠肝脏可溶性和颗粒性制剂的活性。在NaN3激活后，鸟苷酸环化酶活性在Mn2+和Mg2+存在时相似。在NaN3存在的情况下，Co2+作为辅因子部分有效，而Ca2+无论有无NaN3都是一种较差的阳离子。在没有或有1 mM NaN3的情况下，Ba、Cu2+或Zn2+存在时的活性均无法检测到。对于可溶性肝脏酶，在固定的MnGTP或MgGTP浓度为0.4 mM时，锰和镁的活性均依赖于过量的Mn2+或Mg2+；过量Mn2+和Mg2+的表观Km值分别为0.3 mM和0.24 mM。NaN3激活后，活性对游离Mn2+的依赖性降低，对游离Mg2+仍有依赖性，在0.4 mM MgGTP时，过量Mg2+的表观Km值为0.3 mM。用Mn2+或Mg2+测定的可溶性肝脏鸟苷酸环化酶活性随Ca2+的增加而增加。NaN3激活后，Ca2+对Mn2+或Mg2+均无影响或有一定抑制作用。NaN激活后，Ca2+对Mn2+或Mg2+均无影响或有一定抑制作用。NaN2对肝脏或大脑皮层上清液组分中依赖Mn2+和Mg2+的鸟苷酸环化酶活性的刺激作用需要叠氮化钠激活因子的存在。对于部分纯化的可溶性肝脏鸟苷酸环化酶和叠氮化物激活因子，使Mn2+或Mg2+达到半最大激活的NaN3浓度（1 mM）相似。因此，在某些条件下，鸟苷酸环化酶可以有效地将Mg2+用作唯一的阳离子辅因子。
