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ALA dehydratase reaction
The ALA dehydratase reaction occurs in the cytoplasm; the product is porphobilinogen (pronounce).

The substrates are two molecules of ALA.

The reaction is a condensation to form porphobilinogen, the first pyrrole

Two molecules of water are released. The asymmetry of the reaction relative to the two molecules of substrate results in the pyrrole ring having two different substituent groups:

  • acetic acid
  • propionic acid

ALA dehydratase is a -SH containing enzyme

  • It is very susceptible to inhibition by heavy metals, especially lead.
  • increased urinary excretion of its substrate is a good indicator of lead poisoning. Why? (Answer)
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