一种海生单细胞蓝藻的氢酶特点和功能探讨

CHARACTERISTICS AND POSSIBLE FUNCTION OF HYDROGENASE IN A UNICELLULAR MARINE CYANOBACTERIUM

海生单细胞蓝藻,阿格门氏藻,(Agmenellum quadruplicatum strain BG-1)BG-1显示至少含有两种氢酶:吸氢酶——只催化需氧的氢吸收;可逆性氢酶——既催化需光的氢吸收,又催化以还原甲,基紫精为电子供体的氢释放,但活性大不相同。后者为前者的3—5倍。两种氢酶的表达均依赖于藻细胞生长培养基中的镍离子的存在。放氢活性受HgCl_2的强烈抑制,但不受DCMU(敌草隆,后同)和KCN的影响,表明氢酶的氢基团参与催化作用,而该反应既不涉及光合作用的系统Ⅱ,也不涉及呼吸作用的末端电子传递。NaN_3(叠氮钠,后同)强烈地促进整细胞蓝藻的放氢,而对破碎细胞却无明显作用,表明NaN_3有可能通过其它的酶间接作用于可逆性氢酶,超氧离子岐化酶是其中之一。加入NaN_3到整细胞悬液后,超氧离子岐化酶的活性受抑制,并在细胞内积累,反馈抑制还原甲基紫精的自氧化,进而导致可逆性氢酶放氢的促进,显示了超氧离子岐化酶与可逆性氢酶的关系。

The unicellular marine blue-green alga (cyanobacterium) Agmenellum quadruplicatum ttrain BG-1 (Synechococcus ATCC 29404) contained at least two different hydrogenases, she uptake hydrogenase catalyzing only the O2-dependent uptake of H2, the reversible one catalyzing.both hight-dependent hydrogen uptake and high H-evolution with methyl viologen reduced by Na2S2O4 as the electron donor. The expression of both hydrogenase was dependent on Ni+2 in the growth medium. The activity of H2-evolution was strongly inhibited by HgCl, but not by DCMU,KCN and NaN3, suggesting that SH-group in hydrogenase was functioning and neither photosystem II nor terminal electron chain of respiration was involved in the reaction. The hydrogen evolution by intact cells was greatly promoted by addition of azide. We supposed that NaN3 would affect hydrogenase via other relative enzymesexcept through the permeability of the cell envelope. Superoxide dismutase (SOD) was measured. By addition of NaN3 the activity of SOD was repressed, O2 accumulated in the intact cells would be negetive feedback to the autoxidation of reduced methyl viologen, resulting in the promotion of H2-evolution by reversible hydrogenase. Possibly, one of the physiological function of reversible hydrogenase is likely involved in decreation and/or scavengeing of O2 produced in the cell metabolism.