In at least ten species of Lactobacillus, this close homolog to known ornithine decarboxylase occurs in a three-gene neighborhood, along with an amino acid permease family transporter and pyridoxal phosphate-dependent enyzme from the cystathionine gamma-lyase family. Species include L. acidophilus, L. amylovorus, L. crispatus, L. delbrueckii, L. farciminis, L. helveticus, L. johnsonii, etc. The combination of a decarboxylase with an antiporter in a two-gene system suggests a decarboxylation/antiport proton-motive cycle for transient resistance to acidic conditions. The substrate for this decarboxylase might be ornithine but is unknown.
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