title: Phytoecdysteroid C2-hydroxylase is microsomal in spinach, Spinacia oleracea L.
abstract: An enzyme involved in the biosynthesis of phytoecdysteroids, the C2-hydroxylase, has been investigated in spinach, Spinacia oleracea. This enzyme is microsomal and its K(m) has been determined using 2-deoxy-20-hydroxyecdysone as substrate (K(m)=3.72 microM). It is much more efficient with 2-deoxy-20-hydroxyecdysone than with 2-deoxyecdysone and, conversely, the C20-hydroxylase is more active on 2-deoxyecdysone than on ecdysone. These data support the conclusion that C20-hydroxylation precedes C2-hydroxylation. The C2-hydroxylase is inhibited by high concentrations of 20E. Substrate specificity and subcellular localization of C2-hydroxylase differ between plants and insects, and these data, as well as those previously reported on other biosynthetic steps, show the great difference between plant and insect ecdysteroid biosynthetic pathways and suggest an independent origin for the pathways in both kingdoms.
authors.affiliation: UPMC, Université Paris VI, Laboratoire de Biochimie Structurale et Fonctionnelle des Protéines, CNRS FRE 2852, Paris, France.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Bakrim
authors.forename: Emilie
authors.initials: E
authors.lastname: Guittard
authors.forename: Annick
authors.initials: A
authors.lastname: Maria
authors.forename: Jacques Davy
authors.initials: JD
authors.lastname: De Virville
authors.forename: René
authors.initials: R
authors.lastname: Lafont
authors.forename: Najat
authors.initials: N
authors.lastname: Takvorian
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004440:Ecdysone / Q000378:metabolism; D004441:Ecdysterone / Q000096:biosynthesis*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D018724:Spinacia oleracea / Q000737:chemistry / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D010940:Plant Proteins; D004440:Ecdysone; D004441:Ecdysterone; D006899:Mixed Function Oxygenases