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SUMMARY:About the importance of molybdenum for life - Dr Florian Bittner\,
  Technische Universität Braunschweig
DTSTART:20070215T160000Z
DTEND:20070215T170000Z
UID:TALK6019@talks.cam.ac.uk
CONTACT:3901
DESCRIPTION:Abstract The transition element molybdenum (Mo) is of essentia
 l importance for (nearly) all biological systems as it is required by enzy
 mes catalyzing diverse key reactions in the global carbon\, sulfur and nit
 rogen metabolism. In all eukaryotic Mo-containing enzymes the metal is com
 plexed by a pterin\, thus forming the molybdenum cofactor (Moco) which is 
 the active compound at the catalytic site of these enzymes. Moco consists 
 of Mo covalently bound to a unique tricyclic pterin moiety which is synthe
 sized from GTP by an ancient and conserved biosynthetic pathway\, likely b
 eing associated with mitochondria. There are four Moco-containing enzymes 
 in plants: (1) nitrate reductase catalyzes the first and rate-limiting ste
 p in nitrate assimilation and is structurally similar to the recently iden
 tified (2) peroxisomal sulfite oxidase that detoxifies excessive sulfite b
 y simultaneous generation of hydrogen peroxide. (3) Aldehyde oxidase is pr
 esent in several isoforms\, one of which specifically catalyzes the last s
 tep of abscisic acid biosynthesis\, and (4) xanthine dehydrogenase is a ke
 y enzyme of purine degradation and initiation of flowering and leaf senesc
 ence. While nitrate reductase and sulfite oxidase immediately become activ
 e after incorporation of the Moco\, aldehyde oxidase and xanthine dehydrog
 enase require a post-translational sulfuration for activity. This sulfurat
 ion step is catalyzed by the Moco-sulfurase ABA3\, a cytosolic cysteine de
 sulfurase that is regulated by the same stresses like its target enzymes a
 ldehyde oxidase and xanthine dehydrogenase. Besides Moco\, aldehyde oxidas
 e and xanthine dehydrogenase also depend on iron-sulfur clusters as prosth
 etic groups which are synthesised in mitochondria. Analysis of the sta1/at
 m3 mutant of A. thaliana\, which is deficient in a mitochondrial ABC half-
 size transporter responsible for exporting iron-sulfur clusters into the c
 ytosol\, has shown that mitochondria\, and in particular the ATM3 transpor
 ter\, represent a direct crosspoint beween Mo- and iron-homeostasis. \n\nh
 ttp://www.ifp.tu-bs.de/mendel.html
LOCATION:Department of Plant Sciences\, Large Lecture Theatre
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