Proteins with active sites consisting of di-iron centers bridged by oxo or hydroxo groups comprise a new subclass of metalloproteins. This class includes proteins that perform a variety of functions in biology -- dioxygen transport (hemerythrin), oxygen activation (methane monooxygenase), the conversion of ribonucleotides to deoxyribonucleotide (ribonucleotide reductase), and phosphate ester hydrolysis (purple acid phosphatases). This project will focus on the latter two enzymes. Ribonucleotide reductase is the key enzyme in the biosynthesis of deoxyribonucleotide, while purple acid phosphatase may be involved in the regulatory mechanisms of important biological processes. For ribonucleotide reductase, Dr. Que will investigate three aspects: a) the spectroscopic properties of the diferrous form and how it interacts with dioxygen, b) the stoichiometry of tyrosyl radical formation and its implications of cluster- cluster communication via long range electron transfer, and c) the use of cryoenzymological techniques to trap intermediates in the reaction of the di-ferrous form with O2 and spectroscopic characterization of these intermediates. For purple acid phosphatase, experiments will be carried out to test a proposed active site model and a proposed mechanism of enzyme action. Physical techniques to be used include ultra- violet, visible and infra-red spectroscopy, resonance Raman spectroscopy, NMR, EPR, Mossbauer spectroscopy, magnetic circular dichroism and EXAFS.
