Sayavedra-Soto L A, Hommes N G, Russell S A, Arp D J
Laboratory for Nitrogen Fixation Research, Oregon State University, Corvallis 97331-2902, USA.
Mol Microbiol. 1996 May;20(3):541-8. doi: 10.1046/j.1365-2958.1996.5391062.x.
In Nitrosomonas europaea, ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO) catalyse the oxidation of ammonia (NH3) to nitrite (NO2-). A transcript of 3500 bases hybridizes to probes for amoA and amoB (genes that code for AMO proteins). A transcript of 2100 bases hybridizes to probes for hao (the gene that codes for HAO). Induction of the mRNAs detected by amo and hao probes required the presence of ammonium (NH4+). To correlate new levels of mRNA with de novo activity, existent mRNA pools and AMO activity were depleted prior to induction by NH4+. The mRNAs of AMO and HAO were depleted by depriving the cells of energy for at least 8 h; AMO activity was inactivated with acetylene (C2H2) after mRNA depletion. In cells treated this way, levels of new AMO mRNA and de novo AMO enzyme activity were correlated with increased NH4+ concentrations up to 1 mM after 3 h of incubation. HAO mRNA also increased in the NH4(+)-treated cells. Other proteins and RNAs induced by NH4+ were detected in 14CO2-labelling experiments. The AMO and HAO mRNAs were preferentially synthesized during energy-limiting conditions.
在欧洲亚硝化单胞菌中，氨单加氧酶（AMO）和羟胺氧化还原酶（HAO）催化氨（NH₃）氧化为亚硝酸盐（NO₂⁻）。一个3500个碱基的转录本与amoA和amoB（编码AMO蛋白的基因）的探针杂交。一个2100个碱基的转录本与hao（编码HAO的基因）的探针杂交。amo和hao探针检测到的mRNA的诱导需要铵（NH₄⁺）的存在。为了将新的mRNA水平与从头合成的活性相关联，在NH₄⁺诱导之前，先耗尽现有的mRNA库和AMO活性。通过使细胞至少8小时缺乏能量来耗尽AMO和HAO的mRNA；在mRNA耗尽后，用乙炔（C₂H₂）使AMO活性失活。用这种方法处理的细胞，在孵育3小时后，新的AMO mRNA水平和从头合成的AMO酶活性与高达1 mM的NH₄⁺浓度增加相关。在NH₄⁺处理的细胞中，HAO mRNA也增加。在¹⁴CO₂标记实验中检测到了由NH₄⁺诱导的其他蛋白质和RNA。AMO和HAO的mRNA在能量限制条件下优先合成。
