J. C. Dobrowolsk et al.
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case for the so-called glucogenic amino acids (glycine, serine, valine, histidine,
arginine, cysteine, proline, alanine, glutamate, glutamine, aspartate, asparagine, and
methionine). Lysine and leucine are converted to ketone bodies, and are thus called
ketogenic. there is also a group of gluco/ketogenic amino acids (isoleucine, phenylalanine, tryptophan, tyrosine, and threonine) whose hydrocarbon skeleton splits
into two fragments that enter the two pathways independently.
5.2.2 Source of Bioactive Molecules
the amino acids are precursors of many bioactive compounds: active one-carbon
fragments, porphyrins, purine and pyrimidine bases, hormones, neuromediators,
aminoalcohols, biogenic amines, polyamines, carnitine, coenzymes, etc.
Amino acid metabolites often play an important role in signalling. tyrosine hydroxylated at carbon C3 (doPA) is converted in the adrenal gland to catecholamine
hormones and the neurotransmitters epinephrine (adrenaline) and norepinephrine
[8]. Signalling occurs via dopamine, a product of doPA decarboxylation and a neurotransmitter of great importance, since many psychiatric disorders are associated
with the dopamine system.
the decarboxylation of amino acids produces additional biogenic amines beyond dopamine. Among them are γ-aminobutyric acid (GABA) (from glutamate), a
principal inhibitory neurotransmitter; histamine (from histidine), a neurotransmitter
and immune response molecule; and serotonin (from tryptophan via 5-hydroxytryptophan), another neurotransmitter involved in psychiatric disorders [9–12].
other hormones related to tyrosine are triiodothyronine and thyroxine that are
biosynthesised via the modification of tyrosine residues in thyroglobulin.
Not only hormones are produced from amino acids. A local signalling molecule,
nitric oxide, is involved in, inter alia, vessel homeostasis and adaptive vasodilatation, and is made from arginine [13].
Amino acids are also involved in the energetics of cells and organisms. Carnitine,
which transports fatty acids from the cytosol into the mitochondria during the breakdown of lipids, is synthesised from lysine and methionine, while creatine, part of the
phosphocreatine system used to help cells (muscles) meet increased energy demands
during anaerobic effort, is made of L-arginine, glycine, and L-methionine [14, 15].
L-methionine takes part in transmethylation reactions via its metabolite S-adenozylomethionine (SAm) with a highly reactive methyl group [16]. SAm plays a role
in the biosynthesis of polyamines, as well as of dopamine and serotonin. Another
source of active one-carbon fragments is serine, which donates part of its skeleton
to tetrahydrofolate (thF), forming 5-methylotetrahydrofolate (5-mthF), which
subsequently passes its methyl group on to homocysteine to yield methionine [17].
the entire process is called the active methyl cycle. 5-mthF participates also in the
synthesis of purines and thymidine [18].
Amino acids are necessary for the formation of some important structural molecules. the sulphur of cysteine is oxidised, liberated, and conjugated to AtP to form
an active sulphate, a coenzyme in the synthesis of glycosaminoglycan, which builds
86
case for the so-called glucogenic amino acids (glycine, serine, valine, histidine,
arginine, cysteine, proline, alanine, glutamate, glutamine, aspartate, asparagine, and
methionine). Lysine and leucine are converted to ketone bodies, and are thus called
ketogenic. there is also a group of gluco/ketogenic amino acids (isoleucine, phenylalanine, tryptophan, tyrosine, and threonine) whose hydrocarbon skeleton splits
into two fragments that enter the two pathways independently.
5.2.2 Source of Bioactive Molecules
the amino acids are precursors of many bioactive compounds: active one-carbon
fragments, porphyrins, purine and pyrimidine bases, hormones, neuromediators,
aminoalcohols, biogenic amines, polyamines, carnitine, coenzymes, etc.
Amino acid metabolites often play an important role in signalling. tyrosine hydroxylated at carbon C3 (doPA) is converted in the adrenal gland to catecholamine
hormones and the neurotransmitters epinephrine (adrenaline) and norepinephrine
[8]. Signalling occurs via dopamine, a product of doPA decarboxylation and a neurotransmitter of great importance, since many psychiatric disorders are associated
with the dopamine system.
the decarboxylation of amino acids produces additional biogenic amines beyond dopamine. Among them are γ-aminobutyric acid (GABA) (from glutamate), a
principal inhibitory neurotransmitter; histamine (from histidine), a neurotransmitter
and immune response molecule; and serotonin (from tryptophan via 5-hydroxytryptophan), another neurotransmitter involved in psychiatric disorders [9–12].
other hormones related to tyrosine are triiodothyronine and thyroxine that are
biosynthesised via the modification of tyrosine residues in thyroglobulin.
Not only hormones are produced from amino acids. A local signalling molecule,
nitric oxide, is involved in, inter alia, vessel homeostasis and adaptive vasodilatation, and is made from arginine [13].
Amino acids are also involved in the energetics of cells and organisms. Carnitine,
which transports fatty acids from the cytosol into the mitochondria during the breakdown of lipids, is synthesised from lysine and methionine, while creatine, part of the
phosphocreatine system used to help cells (muscles) meet increased energy demands
during anaerobic effort, is made of L-arginine, glycine, and L-methionine [14, 15].
L-methionine takes part in transmethylation reactions via its metabolite S-adenozylomethionine (SAm) with a highly reactive methyl group [16]. SAm plays a role
in the biosynthesis of polyamines, as well as of dopamine and serotonin. Another
source of active one-carbon fragments is serine, which donates part of its skeleton
to tetrahydrofolate (thF), forming 5-methylotetrahydrofolate (5-mthF), which
subsequently passes its methyl group on to homocysteine to yield methionine [17].
the entire process is called the active methyl cycle. 5-mthF participates also in the
synthesis of purines and thymidine [18].
Amino acids are necessary for the formation of some important structural molecules. the sulphur of cysteine is oxidised, liberated, and conjugated to AtP to form
an active sulphate, a coenzyme in the synthesis of glycosaminoglycan, which builds