Obligatory biosynthesis of L-tyrosine via the pretyrosine branchlet in coryneform bacteria

Abstract

Species of coryneform bacteria (Corynebacterium glutamicum, Brevibacterium flavum, and B. ammoniagenes) utilize pretyrosine [fl-(1-carboxy-4-hydroxy-2,5cyclohexadien-1-yl) alanine] as an intermediate in L-tyrosine biosynthesis. Pretyrosine is fonned from prephenate via the activity of at least one species of aromatic aminotransferase which is significantly greater with prephenate as substrate than with either phenylpyruvate or 4-hydroxyphenylpyruvate. Pretyrosine dehydrogenase, capable of converting pretyrosine to L-tyrosine, has been partially purified from all three species. Each of the three pretyrosine dehydrogenases is catalytically active with either nicotinamide adenine dinucleotide or nicotinamide adenine dinucleotide phosphate as cofactors. The Km values for nicotinamide adenine dinucleotide phosphate in C. glutamicum and B. flavum are 55 AM and 14.2 ,uM, respectively, and corresponding Km values for nicotinamide adenine dinucleotide are 350,M and 625,uM, respectively. The molecular weights of pretyrosine dehydrogenase in C. glutamicum and in B. flavum are both about 158, 000, compared with 68,000 molecular weight in B. ammoniagenes. In all three species the enzyme is not feedback inhibited by L-tyrosine. Results obtained with various auxotrophic mutants, which were used to manipulate intemal concentrations of L-tyrosine, suggest that pretyrosine dehydrogenase is expressed constitutively. Pretyrosine dehydrogenase is quite sensitive to p-hydroxymercuribenzoic acid, complete inhibition being achieved at 10 to 25 uM concentrations. This inhibition is readily reversed by thiol reagents such as 2mercaptoethanol. Coryneform organisms, like species of blue-green bacteria,

Purification of arogenate dehydrogenase from Phenylobacterium immobile

“…This dimeric structure is confirmed by another method for determination of the native Mr values of proteins: the cross-linking with dimethylsuberimidate (DMSI) [23]. On a 5% SDS-polyacrylamide gel only two protein bands are detected with h4, values corresponding to monomer and dimer: 38400 + 700 and 68 500 & 1100, respectively, determined by [6]. The pH optimum found for arogenate dehydrogenase was 9.5 in 50 mM glycine/NaOH buffer.…”

Identification of a plant gene encoding glutamate/aspartate‐prephenate aminotransferase: The last homeless enzyme of aromatic amino acids biosynthesis

“…It was then shown mainly by the group of Jensen that depending on the organisms, dehydrogenases and dehydratases dedicated to tyrosine and phenylalanine biosyntheses, respectively, present different specificities for the cyclohexadienyl substrates arogenate or prephenate. Some are exclusively arogenate dependent [6][7][8][9], others exclusively prephenate dependent [10,11], and some are able to use both substrates [11][12][13][14]. This alternative explains the observed great diversity both in terms of organization and regulation in the post-chorismate branch (for reviews, see [4,[15][16][17]).…”

Purification and kinetic analysis of the two recombinant arogenate dehydrogenase isoforms of Arabidopsis thaliana

“…Furthermore, a widespread combination of the alternative routes can be found. For example, in cyanobacteria, and some other microorganisms, both arogenate-totyrosine and phenylpyruvate-to-phenylalanine pathways exist [8][9][10][11][12]. In other bacteria, e.g.…”