CRYSTAL STRUCTURE OF OXIDIZED AND REDUCED PSEUDOAZURIN FROM ACHROMOBACTER CYCLOCLASTES IAM1013. Nobuya Nishio*, Tsuyoshi Inoue*, Shinnichiro Suzuki**, Takamitsu Kohzuma*** and Yasushi Kai*. *Department Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, **Department Chemistry, Faculty of Science, Osaka University, Toyonaka, Osaka 560, ***Department of Chemistry, Faculty of Science, Ibaraki University, Mito, Ibaraki 310, Japan.

The crystal structure of the oxidized and reduced type pseudoazurin from the denitrifying bacteria A. cycloclastes IAM1013 have been solved at 1.6 Å and 2.0 Å resolution respectively. Pseudoazurin from A. cycloclastes (124 amino acid residues; MW 12900 Da) is believed to be electron donor to nitrite reductase which converts nitrite to nitric oxide in the denitrification.

Crystals of the oxidised pseudoazurin were obtained by the hanging-drop vapor diffusion method. The reduction of the crystal carried out by soaking to the solution including sodium ascorbate. The both crystals are isomorphous and belong to orthorhombic space group P212121, cell constants a = 56.69, b = 61.53, c = 30.20 Å. Diffraction data of both crystals were collected on Rigaku R-AXIS IIC. Structure analysis and the following structure refinement have been carried out by molecular replacement method in MERLOT and by X-PLOR and PROLSQ. For the final refined models of the oxidized and reduced pseudoazurin, R-factor were 17.7% and 17.6% respectively.

REFERENCES

1. T. Inoue, N. Nishio, Y. Kai, S. Harada, Y. Ohshiro, S. Suzuki, T. Kohzuma, S. Shidara, H. Iwasaki J. Biochem. 114, 761-762 (1993)

2. T. Inoue, N. Nishio, T. Shimomura, S. Harada, S. Suzuki, T. Kohzuma, S. Shidara, H. Iwasaki, Y. Kai in preparation