Document Detail

Uptake of α-ketoglutarate by citrate transporter CitP drives transamination in Lactococcus lactis.
MedLine Citation:
PMID:  23204417     Owner:  NLM     Status:  MEDLINE    
Transamination is the first step in the conversion of amino acids into aroma compounds by lactic acid bacteria (LAB) used in food fermentations. The process is limited by the availability of α-ketoglutarate, which is the best α-keto donor for transaminases in LAB. Here, uptake of α-ketoglutarate by the citrate transporter CitP is reported. Cells of Lactococcus lactis IL1403 expressing CitP showed significant levels of transamination activity in the presence of α-ketoglutarate and one of the amino acids Ile, Leu, Val, Phe, or Met, while the same cells lacking CitP showed transamination activity only after permeabilization of the cell membrane. Moreover, the transamination activity of the cells followed the levels of CitP in a controlled expression system. The involvement of CitP in the uptake of the α-keto donor was further demonstrated by the increased consumption rate in the presence of L-lactate, which drives CitP in the fast exchange mode of transport. Transamination is the only active pathway for the conversion of α-ketoglutarate in IL1403; a stoichiometric conversion to glutamate and the corresponding α-keto acid from the amino acids was observed. The transamination activity by both the cells and the cytoplasmic fraction showed a remarkably flat pH profile over the range from pH 5 to pH 8, especially with the branched-chain amino acids. Further metabolism of the produced α-keto acids into α-hydroxy acids and other flavor compounds required the coupling of transamination to glycolysis. The results suggest a much broader role of the citrate transporter CitP in LAB than citrate uptake in the citrate fermentation pathway alone.
Agata M Pudlik; Juke S Lolkema
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Publication Detail:
Type:  Journal Article     Date:  2012-11-30
Journal Detail:
Title:  Applied and environmental microbiology     Volume:  79     ISSN:  1098-5336     ISO Abbreviation:  Appl. Environ. Microbiol.     Publication Date:  2013 Feb 
Date Detail:
Created Date:  2013-02-05     Completed Date:  2013-07-08     Revised Date:  2013-08-11    
Medline Journal Info:
Nlm Unique ID:  7605801     Medline TA:  Appl Environ Microbiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1095-101     Citation Subset:  IM    
Top Institute Food and Nutrition, Wageningen, The Netherlands.
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MeSH Terms
Amino Acids / metabolism*
Bacterial Proteins / metabolism*
Ketoglutaric Acids / metabolism*
Lactic Acid / metabolism
Lactococcus lactis / metabolism*
Organic Anion Transporters / metabolism*
Reg. No./Substance:
0/Amino Acids; 0/Bacterial Proteins; 0/Ketoglutaric Acids; 0/Organic Anion Transporters; 328-50-7/alpha-ketoglutaric acid; 50-21-5/Lactic Acid; 77000-09-0/citP protein, Lactococcus lactis

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