Stearoyl-acyl carrier protein delta 9 desaturase from Ricinus communis is a diiron-oxo protein.

• DOI: 10.1073/pnas.90.6.2486
• Publication Date: 2006-05-31T12:41:16Z
• Authors: B G Fox; J Shanklin; C Somerville; E Münck
• Keywords: Acyl carrier protein; Methane Monooxygenase; Ribonucleotide reductase

A gene encoding stearoyl-acyl carrier protein delta 9 desaturase (EC 1.14.99.6) from castor was expressed in Escherichia coli. The purified catalytically active enzyme contained four atoms of iron per homodimer. studied two oxidation states with Mössbauer spectroscopy applied fields up to 6.0 T. These studies show conclusively that the oxidized contains (identical) clusters consisting a pair antiferromagnetically coupled (J > 60 cm-1, H = JS1.S2) Fe3+ sites. diferric cluster exhibited absorption bands 300 355 nm; addition azide elicited charge transfer band at 450 nm. In presence dithionite, were reduced diferrous state. Addition stearoyl-CoA and O2 returned properties are consistent assigning class O2-activating proteins containing diiron-oxo clusters, most notably ribonucleotide reductase methane monooxygenase hydroxylase. Comparison primary structures for these three diverse revealed conserved amino acid sequence -(Asp/Glu)-Glu-Xaa-Arg-His- separated by approximately 100 acids. Since each can catalyze O2-dependent cleavage unactivated C--H bonds, we propose sequences represent biological motif used creation reactive catalytic intermediates. Thus, eukaryotic fatty desaturation may proceed via enzymatic generation high-valent iron-oxo species derived diiron cluster.