title: Kinetics of L-tryptophan production from indole and L-serine catalyzed by whole cells with tryptophanase activity.
abstract: The essential amino acid L-tryptophan can be produced by a condensation reaction between indole and L-serine, catalyzed by whole cells of Escherichia coli B1t-7A with tryptophanase activity. The reaction was previously studied using soluble tryptophanase, a kinetic mechanism proposed and the catalytic properties of the enzyme described. It is important, however, to determine the kinetic parameters of the reaction catalyzed by whole cells, if the process is to be designed with the catalyst in this form. The reaction stoichiometry was established, a mole of product being formed from a mole of each reactant, with no indication of side reactions under the conditions used. The two-substrate reaction kinetics were characterized and modelled, assuming an enzyme-substituted mechanism and no product inhibition. Theoretical consumption rates of indole were compared with experimental values obtained in a batch reactor system. The K(m) values of whole cells towards L-serine and indole were 1.79 M and 0.07 M, respectively. These values are, as expected, considerably higher than their counterparts for soluble tryptophanase.
authors.affiliation: Dept. de Eng. Química e do Ambiente, Escola Superior de Tecnologia, Instituto Politécnico de Tomar, 2300-313 Tomar, Portugal.
authors.forename: Dina Maria Ribeiro
authors.initials: DM
authors.lastname: Mateus
authors.forename: Sebastião Silva
authors.initials: SS
authors.lastname: Alves
authors.forename: Maria Manuela Regalo
authors.initials: MM
authors.lastname: Da Fonseca