title: Reactions of the diiron enzyme stearoyl-acyl carrier protein desaturase.
abstract: Stearoyl-acyl carrier protein Delta(9) desaturase (Delta9D) produces oleic acid, a nutritionally valuable fatty acid containing a cis double bond between C-9 and C-10. This multiprotein diiron enzyme complex reacts with stearoyl-acyl carrier protein, reduced [2Fe-2S] ferredoxin, and O(2) to complete the highly regiospecific and stereoselective desaturation reaction. Interactions with the acyl chain provide stability to the enzyme-substrate complex, give an energetic contribution to catalytic selectivity, and help to order the electron transfer, O(2) binding, and C-H bond cleavage steps of catalysis. Reactions with natural acyl chains indicate the involvement of a highly reactive diiron intermediate capable of oxidizing secondary C-H bonds (bond dissociation energy approximately 95 kcal/mol), but also capable of diagnostic O-atom transfer reactions with the appropriate substrate analogues. For soluble Delta9D, the natural reaction may initiate at the C-10 position, in contrast to the well-established initial reactivity of the membrane enzyme homologue stearoyl-coenzyme A (CoA) Delta(9) desaturase at the C-9 position.
authors.affiliation: Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Fox
authors.forename: Karen S
authors.initials: KS
authors.lastname: Lyle
authors.forename: Corina E
authors.initials: CE
authors.lastname: Rogge
mesh_terms: D000213:Acyl Carrier Protein / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D005287:Ferredoxin-NADP Reductase / Q000737:chemistry / Q000378:metabolism; D005288:Ferredoxins / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D017510:Protein Folding; D017433:Protein Structure, Secondary
chemical_list: D000213:Acyl Carrier Protein; D005288:Ferredoxins; D006899:Mixed Function Oxygenases; C018747:acyl-(acyl-carrier-protein)desaturase; D005287:Ferredoxin-NADP Reductase