The shikimate pathway is the biosynthetic sequence employed by plants and bacteria such as E. coli to generate the aromatic amino acids: phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp):
The red numbers in the chart represent enzymes that catalyze those steps; the blue arrows are transformations that we will not discuss explicitly.
Things to think about:
Here are the first few steps and the enzymes that catalyze the steps:
Most organisms express multiple isozymes of DAHP synthase
|DAHP Synthetase (E. coli; 1kfl), Phe Bound||DAHP Synthetase (Yeast; 1of6), Tyrosine Bound|
Substantial similarity exists among the enzymes from different species
|Sequence Alignment of 1kfl and 1of6||Structure Alignment of 1kfl and 1of6|
This must be a very old biosynthetic pathway.
DQ synthetase also is a dimer in the biologically active state, requiring a Zn++ (purple) and an NAD+ in each unit to function.
It catalyzes a multi-step reaction sequence:
|Proposed Mechanism of Dehydroquinate Synthetase|
What was that about enzymes catalyzing single, specific reactions?
|Dehydroquinate Synthetase, with NAD+and Inhibitor||Catalytic Site of Dehydroquinate Synthetase|