Enzymatic preparation of L-tyrosine and 3,4-dihydroxyphenyl-L-alanine

M379A Mutant Tyrosine Phenol-lyase from Citrobacter freundii Has Altered Conformational Dynamics

The M379A mutant of Citrobacter freundii tyrosine phenol‐lyase (TPL) has been prepared. M379A TPL is a robust catalyst to prepare a number of tyrosines substituted at the 3‐position with bulky groups that cannot be made with wild type TPL. The three dimensional structures of M379A TPL complexed with L‐methionine and 3‐bromo‐dl‐phenylalanine have been determined by X‐ray crystallography. Methionine is bound as a quinonoid complex in a closed active site in 3 of 4 chains of homotetrameric M379A TPL. M379A TPL reacts with l‐methionine about 8‐fold slower than wild type TPL. The temperature dependence shows that the slower reaction is due to less positive activation entropy. The structure of the M379A TPL complex of 3‐bromo‐DL‐phenylalanine has a quinonoid complex in two subunits, with an open active site conformation. The effects of the M379A mutation on TPL suggest that the mutant enzyme has altered the conformational dynamics of the active site.

Genetic incorporation of l-dihydroxyphenylalanine (DOPA) biosynthesized by a tyrosine phenol-lyase

l-Dihydroxyphenylalanine (DOPA) was biosynthesized by a tyrosine-phenol lyase from catechol, pyruvate, and ammonia in Escherichia coli, and the biosynthesized amino acid was directly incorporated into proteins. Three biochemical experiments with mutant proteins containing DOPA confirmed the genetic incorporation of biosynthesized DOPA, and revealed its potential for various biochemical applications.

Thermostable tyrosine phenol-lyase of Symbiobacterium sp. SC-1: gene cloning, sequence determination, and overproduction in Escherichia coli

During the screening for tyrosine phenol-lyase-producing thermophiles, we isolated an obligatory symbiotic thermophile, Symbiobacterium sp. SC-1, which grew only in coculture with Bacillus sp. SK-1. A gene encoding thermostable tyrosine phenol-lyase (TPL) was cloned from the genomic DNA of the Symbiobacterium sp. SC-1 and the nucleotide sequence of the TPL structural gene was determined. The gene consists of 1374 base pairs encoding a polypeptide of 458 amino acid residues; the molecular mass of the enzyme subunit is estimated to be 52,196 Da. The structural gene of TPL was amplified by PCR, blunt-ended, and ligated into the NcoI-HindIII site of plasmid pTrc99A to construct an expression vector for the overproduction of the thermostable TPL. The level of thermostable TPL production was about 15% of the total soluble proteins of Escherichia coli extract. The enzyme was purified to homogeneity from the E. coli extract with an overall yield of 48%.

Free and microencapsulated Erwinia herbicola for the production of tyrosine

Erwinia herbicola (ATCC 21434) was grown in a medium which caused the cells to induce tyrosine phenol-lyase (TPL) activity. Whole cells of Erwinia herbicola were then microencapsulated within alginate-poly-L-lysine-alginate membraned microcapsules (diameter 800 microns). In a rotary shaker-incubator with a 1.9 cm horizontal throw, an agitation rate of at least 240 revolutions per minute (rpm) was required before the TPL activity of the microencapsulated cells was equal to that of the free cells. The TPL activity of the cells, whether free or microencapsulated, could be used for the conversion of ammonia, pyruvate and phenol into tyrosine at 37 degrees C. The results indicate that free cells and microencapsulated cells effect the conversion of these reactants to tyrosine equally well if the agitation rate is 240 rpm. In liver failure the concentrations of both ammonia, phenol and pyruvate are elevated. Hence the TPL activity of microencapsulated Erwinia herbicola could possibly find application in a novel approach for the removal of toxic phenol and ammonia during liver failure.