The fermentation ofb-alanine by Clostridium propionicumproceeds via activation to the CoA-thiol ester, followed by deamination to acryloyl-CoA, which is also an intermediate in the fermentation ofl-alanine. By shifting the organism from the carbon and energy source a-alanine to b-alanine, the enzyme b-alanyl-CoA:ammonia lyase is induced 300-fold ( 30% of the soluble protein). The low basal lyase activity is encoded by theacl1gene, whereas the almost identicalacl2gene (six amino acid substi-tutions) is responsible for the high activity after growth on b-alanine
