THE CRYSTAL-STRUCTURES OF REDUCED PSEUDOAZURIN FROM ALCALIGENES-FAECALIS-S-6 AT 2 PH VALUES

The structures of the reduced (Cu1+) blue-copper protein pseudoazurin from Alcaligenes faecalis strain S-6 are refined at pH 7.8 and 4.4 usi ng X-ray diffraction data to 1.8 Angstrom resolution. The final R-fact ors for the high and low pH structures are 0.178 and 0.177, respective ly. Comparing the reduced pseudoazurin at pH 7.8 with the oxidised (Cu 2+) molecule, small changes are observed in the vicinity of the copper site and on the protein surface. At pH 4.4 the copper substituent imi dazole of His(82) rotates away from the metal with a concurrent moveme nt of the latter towards the plane of the remaining three ligands (Sy- Cys(78), N delta 1-His(40) and S delta-Met(86)) thus the geometry of t he copper site becomes planar trigonal.