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2-1d_his_trp_and_met05

2-1d_his_trp_and_met05 - Biosynthesis of histidine...

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Biosynthesis of histidine, tryptophan, and methionine Tryptophan synthase from S. thyphimurium , showing the tunnel through which indol passes to get from one active site to another
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Histidine biosynthesis is a “fossil” from the “RNA world” Histidine is synthesized from PRPP, ATP, and glutamine PRPP is a common intermediate in the synthesis of purines, pyrimidines, and tryptophan. His residues are often components of enzyme active sites.
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Biosynthesis of trp, tyr, and phe starts with synthesis of chorismate
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QuickTimeª and a decompressor are needed to see this picture. Two of the carbon atoms of tryptophan are derived from PRPP
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Tryptophan synthase contains a protein tunnel connecting two active sites Tryptophan synthase catalyzes the last 2 steps of trp biosynthesis. glyceraldehyde-3-P serine indole-3-glycerol~P-------->indole--------tryptophan α subunit β subunit The enzyme is an α 2 β 2 tetramer ( αββα ). It can be dissociated into 2 α subunits and a β 2 subunit. Τ he α and β active sites are ~ 25A apart The isolated subunits are active but the native enzyme is much faster (>10 X).
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