藍綠藻Anabana HA101其異孢中固氮酶產生氫氣活性及固氮作用之研究

The Hydrogen Evolution Mediated by Nitrogenase in Heterocysts of Filamentous Anabaena HA101

藍綠藻異孢之形成受到硝酸銨所影響，硝酸銨不僅可抑制異孢之分化形成並且可加快已形成異孢之老化作用。固氮酶產生氫氣及固氮作用與異孢之形成有密切之關係。異孢中之固氮酶其產生氫氣之作用受到氮氣之影響，當氮氣存在時，固氮酶產生氫氣之活性減少，相對的，當以Ar取代N2時，固氮酶產生氫氣之活性又增加。固氮酶之固氮作用及產生氫氣之作用均受氧氣所控制，當藍綠藻處於缺氧狀態時，上述固氮酶活性均受到抑制，當藍綠藻再給予氧時，具固氮活性及氫氣產生作用又可恢復。若用KCN處理藍綠藻，具固氮酶活性又受到抑制，但是使用DCMU處理藍綠藻，具固氮酶活性則不受到抑制，可見藍綠藻異孢中之固氮酶具固氮作用及氫氣產生作用均需能源，而此能源則來自異孢之呼吸作用而非來自光合作用。

The heterocyst formations from the initiation and differentiation of vegetative cells of filamentous Anabaena HA 101 were inhibited by the treatment of ammonium nitrate. Besides, those heterocysts, which had already formed along the filaments, could be hastened to degenerate by the ammonium nitrate. The nitrogen fixing (acetylene reducing) and hydrogen evolving activity of nitrogenase localized in heterocysts were closely related with the level of heterocyst formations and heterocyst degenerations. The nitrogenase activity for hydrogen production was decreased while the Anabaena were incubated with a gas mixture containing dinitrogen, which is the substrate of nitrogenase, but the enzyme activity was increased while the Anabaena were grown under a dinitrogen-limited condition. The oxygen was needed for the energy production for the nitrogen fixation and hydrogen evolution mediated by the nitrogenase. Although the Anabaena were treated with a gas mixture containing 20% oxygen, the nitrogenase in heterocysts remained high activities for nitrogen fixation and hydrogen production. The inhibitor, KCN, but not DCMU, suppressed the nitrogenase to reduce acetylene and to evolve hydrogen. This suggests that the energy required for nitrogenase activities was derived from oxidative phosphorylation of respiratory process but was not from the photophosphorylation of photosynthetic process.