Biomedical Engineering Reference
In-Depth Information
Fig. 7.8
Arginine deiminase
catabolism (ADI) in
sourdough lactic acid
bacteria (Adapted from [
3
] ).
1
Arginine-ornithine
antiporter,
2
arginine
deaminase,
3
ornithine
transcarbamylase,
4
carbamate kinase
2-acetyl-pyrroline
baking
ornithine
arginine
1
Out
In
arginine
H
+
2
NH
4
+
citrulline
3
ornithine
Carbamoyl-phosphate
ornithine
H
+
+ ADP
4
ATP
CO
2
+ NH
4
+
Out
pH < 4.4
In
pH = 7
glutamine
glutamine
H
2
O
1
NH
3
NH
3
α
glutamate
glutamate
glutamate
glutamate
α
-ketoglutarate
3
NADH + H
+
H
+
4
2
NAD
+
CO
2
γ
-aminobutyrate
CO
γ
-aminobutyrate
α
-hydroxyglutarate
Fig. 7.9
Glutamine and glutamate metabolism of sourdough lactic acid bacteria.
1
Glutaminase,
2
glutamate decarboxylase,
3
glutamate dehydrogenase,
4
alcohol dehydrogenase
employ aKG as an electron acceptor to regenerate NADH [
20
] . aKG also acts as
the preferred amino acceptor in transamination reactions with leucine, phenylala-
nine, and other amino acids [
72
]. After peptide transport, the transamination reac-
tions are the second limiting factor for the conversion of amino acids by lactic acid
bacteria [
73
]. Consequently, the addition of a-ketoglutarate into the food matrix or
the selection of glutamate dehydrogenase positive strains considerably increases the
