Enzymes from

PRA-isomerase lGP-synthase, a bifunctional enzyme from E. coli that catalyzes two reactions in the synthesis of tryptophan (Figure 4.6), has a polypeptide chain that forms two a/p barrels. The stmcture of this enzyme, solved at 2.8 A in the laboratory of Hans Jansonius in Basel, Switzerland, showed that residues 48-254 form one barrel with IGP-synthase activity, while residues 255-450 form the second barrel with PRA-isomerase activity (Figure 4.7). 

Enzymes for Extreme Conditions. The possibihty of using enzymes from extremophiles, which thrive in oil wells, hot temperatures, freezing conditions, etc, is being explored for the removal of environmental contaminants and survival at extreme temperatures (see Wastes, HAZARDOUS WASTE TREATlffiNT BlORETffiDIATION (SuPPLET NT)). 

Figure Bl.9.9. Comparison of the distance distribution fiinction p(r) of a RNA-polymerase core enzyme from the experimental data (open circle) and the simulation data (using two different models). This figure is duplicated from [27], with pennission from Elsevier Science.

Figure C3.2.17. Diagram of a liposome-based artificial photosynthetic membrane showing the photocycle that pumps protons into the interior of the liposome and the CFqF j-ATP synthase enzyme. From [55],

In Bacillus snbtilis these two reactions are catalyzed by two separate enzymes that have amino acid sequences homologous to the corresponding regions of the bifunctional enzyme from E. coli, and thus each forms a barrel 

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