Metal Cluster Active Sites in Proteins

9405723 Que Proteins with active sites consisting of diiron centers connected by a single oxygen atom bridge and/or carboxylates comprise a new subclass of metalloproteins. This growing class includes dioxygen activating enzymes such as methane monooxygenase, ribonucleotide reductase, and stearoyl ACP delta9 desaturase, and hydrolytic enzymes such as the purple acid phosphatases. A major goal of this proposal is to determine how the diiron sites of the different proteins are interrelated by comparing their spectroscopic properties in the various oxidation states. A second goal, which is specific for the dioxygen activating enzymes, is to understand the mechanisms of oxygen activation by characterizing transient species observed in the reaction of dioxygen with the diiron(II) states of these enzymes. A third goal, which is specific for the purple acid phosphatases, is to determine the roles the two metal centers play in the hydrolytic mechanism. %%% This project is aimed at understanding how a new class of metalloenzymes with active sites consisting of two iron centers catalyzes metabolically important reactions. For example, methane monooxygenase converts methane to methanol under mild conditions, in contrast to the current energy-intensive industrial process. On the other hand, ribonucleotide reductase is responsible for making deoxyribonucleotides, the building blocks of DNA, during cell growth. Using a variety of spectroscopic methods as probes, we will compare the active sites of these enzymes in their various forms to understand their structural relationship, how they catalyze their respective reactions, and the roles of the individual metal centers in carrying out the reactions. ***