CHARACTERISTICS OF TYROSINE PHENOL-LYASE FROM AEROMONAS PHENOLOGENES ATCC 29063

Tyrosine phenol-lyase catalyzes the conversion of L-tyrosine to phenol, pyruvate, and ammonia. The activation energy for the reaction was calculated to be 13,000 calories per mole. The heavy metal Cu⁺⁺ was found to result in a mixed type of inhibition (Ki 0.20 mM). The addition of mercaptoethanol was found to reverse the inhibition by Cu⁺⁺. Competitive inhibition was found with the amino acids L-alanine (Ki18 mM) and L-phenylalanine (Ki 4.4 mM). Phenol, an end product of the tyrosine phenol-lyase reaction, was also found to inhibit enzyme activity (Ki 50 mM). Tyrosine phenol lyase catalyzed the formation of pyruvate from L-tyrosine methyl ester, S-methyl-L-cysteine, and L-serine but at rates lower than with L-tyrosine. Km values for L-tyrosine methyl ester, S-methyl-L-cysteine, and L-serine were found to be 0.37 mM, 0.40 mM, and 1.2 mM, respectively. The reverse reaction by which L-tyrosine is produced from phenol, pyruvate, and ammonia was demonstrated. The pH optimum for the reverse reaction was found to be 9.0 and the Km for phenol 5.0 mM.