ON THE LOCAL-STRUCTURE OF THE GLYCYL RADICAL IN DIFFERENT ENZYMES

Full hyperfine coupling tensors are computed for different geometric c onformers of the glycyl radical, using gradient corrected Density Func tional Theory (DFT) together with large basis sets (IGLO-III). Compari son is made with three enzymes in which the radical is present, namely Escherichia coli pyruvate formate lyase (PFL), Escherichia coli anaer obic ribonucleotide reductase (RNR) and bacteriophage T4 anaerobic RNR . The excellent agreement in hyperfine coupling constants between theo ry and experiment confirms again that the radical is a glycyl radical and that, although embedded in the protein, it maintains the planar ga s phase structure in both E. coli PFL and E. coli RNR. In contrast to these two systems, we propose a non-planar structure for bacteriophage T4 anaerobic RNR, in order to explain the unusually high A(zz)(C-13(a lpha)) coupling (66 G) recently measured by Sjoberg et al.(18).