X-ray absorption spectroscopic studies of the high-spin iron(II) active site of isopenicillin N synthase: evidence for Fe-S interaction in the enzyme-substrate complex

The techniqiue of X-ray absorption spectroscopy was used to examine the coordination of the iron center in isopenicillin N synthase, an Fe2+-dependent enzyme which catalyzes the formation of isopenicillin N from (L-alpha-amino-sigma-adipoyl)-L-cysteinyl-D-valine (ACV), from Cephalosporium acremonium. It was found that the high-spin Fe2+ in the free enzyme is in an approximately octahedral environment consisting of only (N,O)-containing ligands. ACV binding under anaerobic conditions results in the incorporation of a sulfur atom into the iron coordination environment.