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    STUDIA CHEMIA - Issue no. 2 / 2008  
         
  Article:   MECHANISTIC ASPECTS AND BIOCATALYTIC IMPLICATIONS OF THE MIO-CONTAINING AMMONIA-LYASE / AMINOMUTASE FAMILY.

Authors:  LÁSZLÓ POPPE, SAROLTA PILBÁK, CSABA PAIZS, JÁNOS RÉTEY. 		 
       
         
  Abstract:  Histidine, phenylalanine and tyrosine ammonia-lyases (HAL, PAL and TAL) all catalyze ammonia elimination with the aid of a post-translationally formed electrophilic prosthetic group (MIO). MIO occurs also in L-phenylalanine and L-tyrosine aminomutases. Based on the role of PAL as a biocatalyst, the production of ß-phenylalanine analogs can be extended with combined use of ammonia-lyases and amino-mutases. For ammonia-lyases two significantly different mechanisms were suggested. One implies an N-MIO, whereas the second involves a Friedel-Crafts (FC) type intermediate. A common feature of both mechanisms is the formation of a covalent intermediate which allows systematic confomational analysis of the ligand within the rigid active site. Furthermore QM/MM calculations allowed detailed modeling of the alternative covalent intermediates which demonstrated that the N-MIO intermediate has ~140 kcal/mol lower energy than the best FC state.  
         
     
         
         
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