ACTIVE SITE SPECTRAL STUDIES ON MANGANESE METALLOENZYMES

Manganese active sites play a key role in oxygen membolism through
participation in superoxide and peroxide defense mechanisms, oxygen
activation chemistry, and dioxygen biosynthesis. In contrast to
the relatively well-studied Fe and Cu complexes involved in oxygen
chemistry, an sites are just beginning to be studied in details
and the most effective probes have yes to be defined. We plan to
systematically develop a combination of powerful spectroscopic
approaches including optical absorption, CD and low temperature
MCD over the UV-VlS-near IR spectral range complemented by EPR and
SQUID susceptibility measurements to explore the Sround and excited
sites of biological in complexes and probe small molecule
interactions with these active sites. Our initial focus will be
on detailed spectroscopic studies of the mononuclear site in on SD
and the binuclear Mn cluster in Mn pseudocatalase, in all their
accessible redox sites and with exogenous ligand perturbations.
Parallel studied on inorganic models will complement the studied
of manganoenzymes, providing valuable spectral calibration and a
basis for evaluating the information confined in the spectra of the
biological complexes. Manganese coordination complexes
representing each of the key oxidation statues in limiting
geometries for both ononuclear and binuclear Mn will be prepared
and analyzed using the combination of spectroscopies approach for
maximum resolution of the d-->d and charge transfer spectra. This
rich spectral information will be interpreted using powerful
methods of ligand field theory, leading to a description of the
metal ions and their ligand interactions in electronic structural
detail. Key insights developed in the initial studies on this set
of relatively simple and well defined Mn centers will be extended
to the binuclear Mn active site in Mn-dependent ribonucleotide
reductase and the photosynthetic 02-evolving site, providing
information on the structures and ligand interactions in these
important and interesting active sites.