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CHANNELING OF SUBSTRATES AND INTERMEDIATES IN ENZYME-CATALYZED REACTIONS
Ist Teil von
Annual review of biochemistry, 2001-01, Vol.70 (1), p.149-180
Ort / Verlag
Palo Alto, CA 94303-0139: Annual Reviews
Erscheinungsjahr
2001
Link zum Volltext
Quelle
MEDLINE
Beschreibungen/Notizen
The three-dimensional structures of tryptophan synthase, carbamoyl phosphate
synthetase, glutamine phosphoribosylpyrophosphate amidotransferase, and
asparagine synthetase have revealed the relative locations of multiple active
sites within these proteins. In all of these polyfunctional enzymes, a product
formed from the catalytic reaction at one active site is a substrate for an
enzymatic reaction at a distal active site. Reaction intermediates are
translocated from one active site to the next through the participation of an
intermolecular tunnel. The tunnel in tryptophan synthase is ∼25 Å in
length, whereas the tunnel in carbamoyl phosphate synthetase is nearly 100
Å long. Kinetic studies have demonstrated that the individual reactions
are coordinated through allosteric coupling of one active site with another.
The participation of these molecular tunnels is thought to protect reactive
intermediates from coming in contact with the external medium.