More than a third of proteins use a metal ion to ensure their function, and this metal ion may have a structural or catalytic role. One of the most important advances in the field of metals in biology over the last decade has been the discovery of complex, metal-specific machineries that regulate the homeostasis of individual metal ions within cells. Paradoxically, during the same period, several enzymes have been discovered that can function with different metals, iron and/or manganese, in the same active site : this is the case of purple acid phosphatases and ribonucleotide reductases for binuclear active site enzymes.
The first part of the presentation focused on the iron-manganese duality, based on the specific properties of the two metals. This duality was developed in the case of several enzymes using both metals indifferently at the same active site, and a rationalization of the functional impact of iron-manganese substitution was outlined.
This rationalization was illustrated in the following two sections, which presented the activities of synthetic binuclear complexes possessing Fe2, FeMn or Mn2 sites. In the first part, the activity of the compounds in the hydrolysis of phosphate ester functions was described and discussed in terms of the intrinsic properties of the metals involved. Secondly, a similar presentation of their reactivities with hydrogen peroxide showed the differences in behavior of each system. Finally, the various aspects of iron-manganese substitution highlighted were placed in the context of cellular stress situations in the light of recent in vivo studies.
