Diaminopropionate ammonia-lyase from Salmonella typhimurium. Purification and characterization of the crystalline enzyme, and sequence determination of the pyridoxal 5'-phosphate binding peptide

We have found a wide occurrence of alpha,beta-diaminopropionate ammonia-lyase in bacteria and actinomycetes. Considerable amounts of this enzyme were found in Salmonella typhimurium. The enzyme was purified and crystallized from S. typhimurium (IFO 12529). The relative molecular mass of the native enzyme, estimated by the ultracentrifugal equilibrium method, is 89,000 Da, and the enzyme consists of two subunits identical in molecular mass. The enzyme exhibits absorption maxima at 278 and 413 nm and contains 2 mol of pyridoxal 5'-phosphate(pyridoxal-P)/mol of enzyme. The enzyme catalyzes the alpha,beta-elimination reaction of both L- and D-alpha,beta-diaminopropionate, the most suitable substrates, to form pyruvate and ammonia. The L- and D-isomers of serine were also degraded, though slowly. After the internal Schiff base with pyridoxal-P had been reduced with sodium borohydride, followed by trypsin or lysyl endopeptidase digestion of the enzyme, we determined the sequence of about 20 amino acid residues around the lysine residue which binds pyridoxal-P. No homology was found in either the amino acid sequence of the pyridoxal-P binding peptide or the amino-terminal amino acid sequence between the enzyme and other pyridoxal-P-dependent enzymes.