ABSTRACT
Structural studies of the Fe and Mn forms of the cambialistic enzyme from P. shermanii revealed structures that were almost identical [96]. The tertiary structure of this enzyme hardly differs from the strictly Fe-dependent and strictly Mn-dependent enzymes. The metal coordination sphere of the iron and manganese ions in the enzyme is trigonal bipyramidal, and it is evident that structural differences between the manganese and iron form cannot explain the cambialistic behavior. EXAFS mea surements on the Fe form of this enzyme suggest that the coordination number changes to six with increasing pH [99]. Binding of N3 to the iron causes the iron to become six-coordinate over the entire pH range [100].
