Dehydroalanine in Histidine Ammonia Lyase

Preparations of highly purified Pseudomonas histidine ammonia lyase were inactivated by reduction with sodium borotritide. Alanine was the only labeled material in acid hydrolysates of the dialyzed product. Its presence indicates the presence of dehydroalanine (2-aminoacrylic acid) in the enzyme. There was approximately 0.9 mole of labeled alanine per mole of enzyme. Enzyme inactivation and tritium incorporation into alanine were largely prevented by the presence of histidine. This result suggests that dehydroalanine is at the active site of histidine ammonia lyase.