Transamination catalysed by tyrosine phenol‐lyase from Citrobacter intermedius

The interactions of tyrosine phenol‐lyase with its substrates: l‐tyrosine and l‐serine, and the competitive inhibitors: l‐alanine, l‐phenylalanine, l‐m‐tyrosine, were studied. It was demonstrated that the enzyme catalyzed a half‐transamination reaction between substrates or inhibitors and the protein‐bound pyridoxal phosphate. The products of this side‐reaction, pyridoxamine phosphate and the respective keto acids, were identified. The kinetic parameters were determined for β‐elimination of l‐tyrosine and of l‐serine, and for the transamination of l‐serine and the inhibitors used. The transfer of the amino group to the coenzyme takes place in the direction from amino acid to pyridoxal phosphate, but not in the opposite direction, i.e. the transamination is irreversible.