Chemistry Reference
In-Depth Information
13.6.1.
Functions of Vitamin B6
In general, PLP serves mainly as a co-enzyme for about 100 enzymes in
amino acid metabolism (Bitsch, 1993). It is bound covalently to its enzyme by
a Schiff base with an
"
-amino group of lysine in the enzyme. During the
enzymatic reaction, the amino group of the substrate and the aldehyde group
of PLP form a Schiff base. All subsequent reactions can occur at the
-,
-or
-C of the respective substrate. In the following, a brief list of common
reaction types is given; for more details the reader is referred to specific
literature (e.g. Leklem, 2001; Frank, 2002a):
Transamination (transfer of the amino group of one amino acid to
the keto analogue of another amino acid)
Decarboxylation (resulting in biogenic amines)
-or
-elimination
PMP acts exclusively as a co-enzyme for transaminases:
1. Transferase
a. Serine hydroxymethyl transferase (C1 metabolism)
b.
D
-aminolevolunate synthase (porphyrin biosynthesis)
c. Glycogen phosphorylase (glycogen mobilization)
d. Aspartate aminotransferase (transamination)
e. Alanine aminotransferase (transamination)
2. Oxidoreductase
a. Lysyl oxidase (collagen biosynthesis)
3. Hydrolase
a. Kynureninase (niacin biosynthesis)
4. Lyase
a. Glutamate decarboxylase (GABA synthesis)
b. Tyrosine decarboxylase (tyramine biosynthesis)
c. Serine dehydratase (
-elimination)
d. Cystathionine
-synthase (methionine metabolism)
e. Cystathionine
-lyase (
-elimination)
Due to its role as a co-enzyme in amino acid metabolism (see below),
vitamin B6 has a broad range of functions in many systems of the body,
including the immune system, the nervous system, gluconeogenesis, lipid
metabolism, erythrocyte function, hormone modulation, gene expression
and niacin formation. In the immune system, as an example, vitamin B6
increases the immune response of critically ill patients (Cheng et al., 2006)
