Mössbauer investigation of the cofactor iron of putidamonooxin

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Abstract
Mononuclear non-heme cofactor Fe in putidamonooxin was investigated in the binary oxidized ''enzyme.cntdot.substrate'' complex and in the ternary ''enzyme.cntdot.substrate.cntdot.NO'' complex via Moessbauer spectroscopy. The experimental spectra were analyzed on the basis of the spin-Hamiltonian formalism. The resulting fine and hyperfine structure parameters are compared with literature values of similar compounds. From this comparison it was concluded that in the binary complex (reduced and oxidized) the mononuclear non-heme cofactor Fe has a coordination number > 4. The cofactor Fe shows remarkable spectral similarities with Fe in protocatechuate 3,4-dioxygenase, though the catalytic properties of the Fe sites in the 2 proteins are different. The data obtained from the ternary ''enzyme.cntdot.substrate.cntdot.NO'' complex indicate that the cofactor Fe is in the ferric intermediate spin state (S = 3/2) and is pentacoordinated, which means that upon NO binding to the reduced cofactor Fe at least 1 ligand has to be released. Comparing these data with literature values suggests that the cofactor Fe in the binary as well as in the ternary NO complex is not directly bound to a S atom, though biochemical arguments seem to indicate the opposite.