%0 Journal Article %A Smith, Andrew %A Hill, Susan %A Anthony, Christopher %T The purification, characterization and role of the d-type cytochrome oxidase of Klebsiella pneumoniae during nitrogen fixation %D 1990 %J Microbiology, %V 136 %N 1 %P 171-180 %@ 1465-2080 %R https://doi.org/10.1099/00221287-136-1-171 %I Microbiology Society, %X Klebsiella pneumoniae synthesized only b-type and d-type cytochromes under the wide range of growth conditions tested, and reaction with CO revealed two potential oxidases. The o-type oxidase was produced only in the presence of O2 and appeared to be repressed by glucose. The d-type oxidase was, by contrast, produced only in the absence of measurable O2 (< 1μm), and was the only oxidase expressed in nitrogen-fixing conditions. It was extracted from the membrane, purified and shown to be similar to that from E. coli in being a heterodimer (subunits of M r 52000 and 35000), in containing two distinguishable b haems and haem d (one or two molecules per molecule of oxidase), and in being able to react with O2 to give a stableoxygenated intermediate. The purified d-type cytochrome oxidase had a very high affinity for O2 (K m 20 nm; measured by the spectral properties of leghaemoglobin). It is proposed that this provides a role for this oxidase in lowering the O2 concentration to allow nitrogenase synthesis and function, and to provide a terminal oxidase to permit electron-transport-coupled ATP synthesis which supports the increase in efficiency of nitrogen fixation observed under microaerobic conditions. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-136-1-171