Corynebacterium glutamicum - JUWEL - Forschungszentrum Jülich

2. Theory
proteome14 (Hermann et al., 2001) and the metabolome15 (Chassagnole et al., 2003;
Drysch et al., 2003; Park et al., 1997; Sahm et al., 2000; Vallino and Stephanopoulos,
1993; Varela et al., 2003; Wittmann and Heinzle, 2001) are thoroughly investigated.
This also resulted in the availability of many tools for genetic modifications of
C. glutamicum (Nampoothiri and Pandey, 1998).
C. glutamicum needs biotin for growth, which was an important characteristic because
the glutamate production was triggered by biotin limitation in wild-type strains
(Shiio et al., 1962). Nowadays, with modern biotechnological techniques, also other
growth limitations and other mechanisms are available to achieve overproduction of
amino acids (Kimura, 2002), as is also the case in the organism which is used in the
current study.
Another characteristic of C. glutamicum, which may be of importance for its use, is the
complex cell envelope containing mycolic acids (Bayan et al., 2003; Christensen et al.,
1999), which are typical for Corynebacteriaceae, Mycobacteriaceae, Nocardiaceae and a
few small other families (Glazer and Nikaido, 1995). These mycolic acids form an extra
hydrophobic barrier which probably causes the low permeability of the cell wall for
hydrophilic compounds (Jarlier and Nikaido, 1990). Hydrophilic compounds therefore
have to pass the cell wall through a channel (Costa-Riu et al., 2003a,b).
CH3 COO
H3C -
L-Valine is a natural proteinogenic amino
acid and it is one of the essential amino acids
for humans. Together with leucine and alanine,
it forms the pyruvate family of amino
acids. Furthermore, it is a branched chain
amino acid just like leucine and isoleucine.
It is a fairly hydrophobic (logp =1.64), neutral
amino acid (pI=5.96), which makes it
NH +
3
likely that it may be able to pass the cell
membranes relatively good through passive
diffusion (Krämer, 1994). The structure of
Figure 2.5.: L-Valine
L-valine is shown in figure 2.5.
The annual production of L-valine is
about 1000 tons, which is among the smaller amounts for natural proteinogenic amino
acids (Drauz et al., 2003; Eggeling et al., 2001; Leyval et al., 2003). It is mainly being
used in infusion fluids and special dietary nutrition. However, also beneficial effects
of addition of L-valine to pig- and chicken feed were reported (Boyd et al., 2000;
Harms and Russell, 2001; Kidd et al., 2000).
L-Valine is currently being produced by isolation from protein hydrolysates,
in fermentative processes or by enzymatic resolution of N-acetyl-D,L-valine
14 The proteome indicates the proteins which are present in the cells.
15 The intracellular concentration of metabolites: intermediates and products of metabolic pathways.
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