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Figure 7.
FIG. 7. The active sites of ALS and AHAS. A shows the
active site region of K. pneumoniae ALS (resting enzyme), and B
shows the active site of yeast AHAS viewed in a similar
orientation. Residues with and without the prime symbol are
derived from different monomers. C, the active site of ALS is
shown with the second molecule of pyruvate modeled in so that it
makes favorable contacts and is orientated so that it would
yield the S-enantiomer of acetolactate (D). In this model, the
intermediate is represented as the tricyclic carbanion (IVb,
Fig. 5), and an alternate conformation of Lys36 is shown for
which the  -amino group forms an
ionic interaction with the carboxylate of the second pyruvate.
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