Maier R J, Hanus F J, Evans H J
J Bacteriol. 1979 Feb;137(2):825-9. doi: 10.1128/jb.137.2.825-829.1979.
Factors that regulate the expression of an H2 uptake system in free-living cultures of Rhizobium japonicum have been investigated. Rapid rates of H2 uptake by R. japonicum were obtained by incubation of cell suspensions in a Mg-phosphate buffer under a gas phase of 86.7% N2, 8.3% H2, 4.2% CO2, and 0.8% O2. Cultures incubated under conditions comparable with those above, with the exception that Ar replaced H2, showed no hydrogenase activity. When H2 was removed after initiation of hydrogenase derepression, further increase in hydrogenase activity ceased. Nitrogenase activity was not essential for expression of hydrogenase activity. All usable carbon substrates tested repressed hydrogenase formation, but none of them inhibited hydrogenase activity. No effect on hydrogenase formation was observed from the addition of KNO3 or NH4Cl at 10 mM. Oxygen repressed hydrogenase formation, but did not inhibit activity of the enzyme in whole cells. The addition of rifampin or chloramphenicol to derepressed cultures resulted in inhibition of enzyme formation similar to that observed by O2 repression. The removal of CO2 during derepression caused a decrease in the rate of hydrogenase formation. No direct effect of CO2 on hydrogenase activity was observed.
对调节日本根瘤菌自由生活培养物中H2摄取系统表达的因素进行了研究。通过将细胞悬浮液在含有86.7% N2、8.3% H2、4.2% CO2和0.8% O2的气相下于磷酸镁缓冲液中孵育，可获得日本根瘤菌快速的H2摄取速率。在与上述条件相当的条件下培养，但用Ar代替H2，培养物未显示出氢化酶活性。在氢化酶去阻遏开始后去除H2，氢化酶活性的进一步增加停止。固氮酶活性对于氢化酶活性的表达不是必需的。测试的所有可用碳底物均抑制氢化酶的形成，但它们均未抑制氢化酶活性。添加10 mM的KNO3或NH4Cl对氢化酶的形成没有影响。氧气抑制氢化酶的形成，但不抑制全细胞中该酶的活性。向去阻遏的培养物中添加利福平或氯霉素会导致酶形成受到抑制，类似于氧气抑制所观察到的情况。在去阻遏过程中去除CO2会导致氢化酶形成速率降低。未观察到CO2对氢化酶活性的直接影响。
