四唑(Tetrazolium)对固氮鱼腥藻固氮和氢代谢的影响

固氮鱼腥藻(Anabaena azotica Ley)细胞能还原无色的TTC和NBT分别成为红色或蓝色的甲(月朁)(formazan)沉淀。异形胞还原TTC的速率高于营养细胞。前异形胞及异形胞附近的营养细胞对NBT的还原作用最强。而异形胞对NBT不起还原作用。无论在异形胞形成红色甲(月朁)或在营养细胞形成蓝色甲(月朁)后都抑制固氮酶活性。NBT甲(月朁)对固氮酶活性的抑制作用大于TTC甲(月朁),因为NBT氧化还原电位低于TTC。 TTC和NBT两者都明显地抑制固氮鱼腥藻完整细胞的放氢。因鱼腥藻的放氢是由固氮酶催化的结果。四唑抑制放氢推想是由于它截取了固氮酶催化系统中的电子的缘故。固氮微生物(包括蓝色细菌和根瘤菌)对四唑还原与吸氢酶之间有无相关是一个争论的问题。一些学者认为分离豆科植物体的一些根瘤菌株培养于含有TTC的琼脂培养基,如还原,便可证明这些根瘤菌株能氧化氢;换言之,应用TTC的还原可作为一些根瘤菌的菌落具有吸氢酶的验证。相反,我们发现固氮鱼腥藻还原TTC和NBT之后,都没有影响吸氢的能力。因此,我们推想固氮鱼腥藻对四唑之还原与吸氢酶是没有直接的关系。

EFFECT OF TETRAZOUUM ON NITROGEN FIXATION AND HYDROGEN METABOLISM IN ANABAENA AZOTICA LEY

The cells of Anabaena azotica reduce the colourless TTC and NBT into red or blue water-insoluble formazans respectively. Heterocysts reduce TTC faster than the vegetative cells. NBT has revealed the strongest reducing power in proheterocysts and vegetative cells next to heterocysts. There is none of reduced NBT in heterocysts.Both red formazan deposition in heterocysts and blue-formazan formation in vegetative cells inhibit nitrogenase activity. The NBT formazan more inhibits the nitrogenase activity than TTC formazan, because the potential redox of NBT is lower than TTC.Both TTC and NBT conspicuously inhibit hydrogen evolution, as a result of catalysis of nitrogenase in intact cells of Anabaena azotica. It is considered that tetrazolium intercepts the electrons from the system catalyzed by nitrogenase.There is controversy about the relationship between tetrazolium reduction and uptake hydrogenase activity in nitrogen fixing organisms (Cyanobacteria and Rhizobia). Some scientists consider that the reduction of TTC in agar medium is used to dectect strains of free living Rhizobia capable of oxidizing H_2, that is use of TTC as a method for detecting colonies with uptake hydrogenase is advantageous. On the contrary, we discover that after reducing TTC and NBT by Anabaena azotica there is no effect on H_2-uptake capacity. So we suppose that the reduction of tetrazolium does not directly relate to uptake hydrogenase.