Pseudomonas thiazolinophilum

In 1978 the conversion of the racemic 2-amino-d2-thiazoline-4-carboxylic acid into L-cysteine, catalysed by Pseudomonas thiazolinophilum cells, was reported [92]. Due to a racemase the overall process is a dynamic kinetic resolution and yields of 95% are obtained in the industrial process (Scheme 6.26) [34]. 

Scheme 6.26 Ajinomoto produces L-cysteine with 30 g 1 1 via a Pseudomonas thiazolinophilum-catalysed process. ...

Much of the world s cysteine is isolated from keratin, mostly obtained in the form of hair. The process, which is based on an acid hydrolysis of the protein, is smelly, and it produces waste products which are difficult to treat. It is progressively being replaced by an enzymatic synthesis which once again couples a stereospecific hydrolysis with a racemisation process. Methyl-2-chloroacrylate is converted into DL-amino-A2-thiazoline-4-carbo-xylate, and both enantiomers of this intermediate are then hydrolysed by an enzyme from Pseudomonas thiazolinophilum or Sarcina lutea directly to L-cysteine. The necessary racemisation occurs spontaneously during the reaction (Scheme 6.10). 

Pseudomonas thiazolinophilum A] 3854 is known to quantitatively convert ( )-2-amino-4,5-dihydrothiazoline-4-carboxyhc acid to (R)-cysteine in 100% ee... 

Degradation of L-cysteine by cysteine desulfhydrase or other PLP enzymes present in the cells was successfully prevented by addition of hydroxylamine or semi-carbazide to the incubation mixture. A mutant strain of Ps. thiazolinophilum lacking cysteine desulfhydrase was isolated and used to produce L-cysteine from d,l-ATC in a molar yield of 95% and at a product concentration of 31.4 g L 1[12S. Pseudomonas desmolytica A] 3872, one of the L-cysteine producers isolated was found to lack the ability to convert d-ATC into L-cysteine it is an ATC racemase-deficient strain 129l. However, little is known about the enzymological properties and function of the racemase. 

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