Two-Dimensional Structure of Membrane-Bound Nitrite Oxidoreductase from Nitrobacter hamburgensis

Author： Spieck E. Muller S. Engel A. Mandelkow E. Patel H. Bock E.

ISSN： 1047-8477

Source： Journal of Structural Biology, Vol.117, Iss.2, 1996-09, pp. : 117-123

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Abstract

Isolated membranes of the facultative nitrite oxidizing bacterium Nitrobacter hamburgensis X 14 displayed a periodic arrangement of the membrane-bound nitrite oxidoreductase (NOR). The crystallinity of these two-dimensional NOR arrays was improved by polyethylene glycol treatment. Negative stain electron microscopy and digital image processing were used to analyze the structure of NOR. The lattice vectors had a length of 9.7 ± 0.4 and 11.8 ± 0.4 nm, including an angle of alpha = 71#°. Diffraction patterns of the oblique lattice extended to the third order indicating a resolution of ~2.9 nm. The correlation averaged projection suggested a twofold symmetric unit cell composed of two enzyme particles with an asymmetric shape, showing a larger and a smaller morphological domain. The molecular weight of a single NOR particle was found to be 186 ± 43 kDa by scanning transmission electron microscopy, suggesting that this particle is an alphabeta-heterodimer.