Solvent accessibility, high-potential iron

High-potential iron proteins, 45 313-314, 344 cluster stability, 45 324-332 function, 45 315-316 residues, 45 322-344 structure and, 45 317-322 redox properties, 45 333-344 solvent accessibility, 45 330, 332-333 source and function, 45 314-316 structure, 45 316-322 hydrogen bonding and, 45 321-322 intermolecular aggregation, 45 322 primary, 45 317-318 secondary and tertiary, 45 318-321... 

Fluorine-labeled analogues of C. vinosum high-potential iron protein have been investigated by F NMR spectroscopy. By incorporation of specific fluorine-labeled amino acid residues, one can insert unique probes at well-defined locations within the protein core. The synthesis and purification of 2-, 3-, and 4-fluorophenylalanine (abbreviated 2-F-, 3-F-, and 4-F-Phe, respectively), 3-fluorotyrosine (3-F-Tyr), and 5-fluorotr3q)tophan (5-F-Trp) derivatives of C. vinosum HiPIP, the assignment of F NMR resonances, the measurement of longitudinal relaxation times, and the temperature dependence of F and resonances have all been reported 42, 43, 136). These measurements were used to examine structural perturbations of mutants, the dynamics of interaction of residues with the cluster, and solvent accessibility, and as a test of the relative contribution of cross-relaxation to magnetization decay. 

The conclusion from these studies is that neither specific aromatic amino acid side chains nor solvent accessibility appear to play a major role in defining the reduction potentials or electron transfer properties of the cluster in high-potential iron proteins. The role of the aromatic core is to maintain a hydrophobic barrier to solvent water and inhibit oxidation and hydrol5 ic degradation of the cluster. 

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