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Applied and Environmental Microbiology, November 1999, p. 4873-4880, Vol. 65, No. 11
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Genetic Characterization of the Major Lactococcal Aromatic Aminotransferase and Its Involvement in Conversion of Amino Acids to Aroma Compounds

Liesbeth Rijnen,1 Sophie Bonneau,2 and Mireille Yvon1,*

Unité de Recherches de Biochimie et Structure des Protéines1 and Laboratoire de Génétique Microbienne,2 INRA, 78352 Jouy-en-Josas Cedex, France

Received 25 January 1999/Accepted 17 August 1999

In lactococci, transamination is the first step of the enzymatic conversion of aromatic and branched-chain amino acids to aroma compounds. In previous work we purified and biochemically characterized the major aromatic aminotransferase (AraT) of a Lactococcus lactis subsp. cremoris strain. Here we characterized the corresponding gene and evaluated the role of AraT in the biosynthesis of amino acids and in the conversion of amino acids to aroma compounds. Amino acid sequence homologies with other aminotransferases showed that the enzyme belongs to a new subclass of the aminotransferase I subfamily gamma ; AraT is the best-characterized representative of this new aromatic-amino-acid-specific subclass. We demonstrated that AraT plays a major role in the conversion of aromatic amino acids to aroma compounds, since gene inactivation almost completely prevented the degradation of these amino acids. It is also highly involved in methionine and leucine conversion. AraT also has a major physiological role in the biosynthesis of phenylalanine and tyrosine, since gene inactivation weakly slowed down growth on medium without phenylalanine and highly affected growth on every medium without tyrosine. However, another biosynthesis aromatic aminotransferase is induced in the absence of phenylalanine in the culture medium.

* Corresponding author. Mailing address: Unité de Recherches de Biochimie et Structure des Protéines, INRA, Centre de Recherches de Jouy-en-Josas, Domaine de Vilvert, 78352 Jouy-en-Josas, Cedex, France. Phone: 33 1 34 65 21 59. Fax: 33 1 34 65 21 63. E-mail: Mireille.Yvon{at}diamant.jouy.inra.fr.

Applied and Environmental Microbiology, November 1999, p. 4873-4880, Vol. 65, No. 11
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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