12 Small Nitrogenous Compounds
12.1
12.1.1
12.1.2
12.1.3
12.2
12.3
12.4
12.4.1
12.4.2
12.4.3
12.4.4
12.4.5
12.4.6
12.5
12.5.1
12.5.2
12.5.3
12.5.4
12.5.5
12.6
Free Amino Acids
The Chemical Nature of Free Amino Acids
Concentration and Spectrum of the Free Amino
Acids
Osmotic Functions of Small Nitrogenous
Compounds
Nutritional Aspects of Amino Acid Metabolism
End Products of Nitrogen Metabolism
Nitrogen Metabolism of the Amino Acids
L-Amino Acid Oxidases
Aminotransferases (Transaminases)
Glutamate Dehydrogenases
Glutamine Synthetases and Glutaminases
Production of Ammonia
Urea Synthesis
Metabolism of Individual Amino Acids
Proline
Sulphur-Containing Amino Acids
Serine
Tryptophan
Iodamino Acids
Aromatic Amino Acids and the Sclerotization
of Insect Cuticulae
u.t Free Amino Acids
Because of the constant turnover of proteins,
protein-bound and free amino acids exist in a
dynamic equilibrium. The intracellular pool of
free amino acids, which is replenished by the
hydrolysis of existing proteins, by uptake from
the intercellular space and by de novo synthesis,
is available for protein synthesis and for the many
other metabolic processes dependent upon amino
acids. The concentration of free amino acids is
always lower than that of the protein-bound residues, one limiting factor being the strong osmotic
effects of such low molecular weight compounds.
Thus, there is no specific amino acid store in an
organism; it is more the case that enzymes and
structural proteins themselves represent the
reserve of amino acids. Insect larvae, which
require large amounts of amino acids for meta12.6.1
12.6.2
12.6.3
12.7
Sclerotizing Substances
The Process of Sclerotization
Phenoloxidases
o-Amino Acids and Their Metabolism
12.8
Amines
12.8.1 N-Methylated Bases
12.8.2 Amines Derived from Tyrosine, Tryptophan
and Histidine
12.8.3 Polyamines
12.9
Phosphagens and Other Guanidine Compounds
12.9.1 Biosynthesis and Occurrence
12.9.2 Phosphagen Kinases
12.10 Oligopeptides and Their Metabolism
12.10.1 Glutathione
12.10.2 Histidine Peptides
12.11 Purine and Pyrimidine Compounds
12.11.1 Biosynthesis of Purine Nucleotides
12.11.2 Adenylate and Guanylate Cyclases
12.11.3 Catabolism of Purine Nucleotides
and Uric Acid Synthesis
12.11.4 Uricolysis
12.11.5 Metabolism of Pyrimidine Nucleotides
References
morphosis and sclerotization of the cuticula,
make use of extracellular proteins as a source of
amino acids; examples include the larval haemolymph proteins of some dipterans (p.191) and
possibly the haemoglobins of the non-biting
midges (Chironomidae) (p.273).
12.1.1 The Chemical Nature of Free Amino
Acids
As the biosynthesis of cell proteins requires 20
standard amino acids, these must all be present in
the pool of free amino acids. Previous publications about certain organisms or tissues in which
fewer amino acids were typically found were
based upon the insufficiently sensitive methods of
paper and thin-layer chromatography. In addition
to the standard amino acids, the pool of small nit-
12.1
12.1.1
12.1.2
12.1.3
12.2
12.3
12.4
12.4.1
12.4.2
12.4.3
12.4.4
12.4.5
12.4.6
12.5
12.5.1
12.5.2
12.5.3
12.5.4
12.5.5
12.6
Free Amino Acids
The Chemical Nature of Free Amino Acids
Concentration and Spectrum of the Free Amino
Acids
Osmotic Functions of Small Nitrogenous
Compounds
Nutritional Aspects of Amino Acid Metabolism
End Products of Nitrogen Metabolism
Nitrogen Metabolism of the Amino Acids
L-Amino Acid Oxidases
Aminotransferases (Transaminases)
Glutamate Dehydrogenases
Glutamine Synthetases and Glutaminases
Production of Ammonia
Urea Synthesis
Metabolism of Individual Amino Acids
Proline
Sulphur-Containing Amino Acids
Serine
Tryptophan
Iodamino Acids
Aromatic Amino Acids and the Sclerotization
of Insect Cuticulae
u.t Free Amino Acids
Because of the constant turnover of proteins,
protein-bound and free amino acids exist in a
dynamic equilibrium. The intracellular pool of
free amino acids, which is replenished by the
hydrolysis of existing proteins, by uptake from
the intercellular space and by de novo synthesis,
is available for protein synthesis and for the many
other metabolic processes dependent upon amino
acids. The concentration of free amino acids is
always lower than that of the protein-bound residues, one limiting factor being the strong osmotic
effects of such low molecular weight compounds.
Thus, there is no specific amino acid store in an
organism; it is more the case that enzymes and
structural proteins themselves represent the
reserve of amino acids. Insect larvae, which
require large amounts of amino acids for meta12.6.1
12.6.2
12.6.3
12.7
Sclerotizing Substances
The Process of Sclerotization
Phenoloxidases
o-Amino Acids and Their Metabolism
12.8
Amines
12.8.1 N-Methylated Bases
12.8.2 Amines Derived from Tyrosine, Tryptophan
and Histidine
12.8.3 Polyamines
12.9
Phosphagens and Other Guanidine Compounds
12.9.1 Biosynthesis and Occurrence
12.9.2 Phosphagen Kinases
12.10 Oligopeptides and Their Metabolism
12.10.1 Glutathione
12.10.2 Histidine Peptides
12.11 Purine and Pyrimidine Compounds
12.11.1 Biosynthesis of Purine Nucleotides
12.11.2 Adenylate and Guanylate Cyclases
12.11.3 Catabolism of Purine Nucleotides
and Uric Acid Synthesis
12.11.4 Uricolysis
12.11.5 Metabolism of Pyrimidine Nucleotides
References
morphosis and sclerotization of the cuticula,
make use of extracellular proteins as a source of
amino acids; examples include the larval haemolymph proteins of some dipterans (p.191) and
possibly the haemoglobins of the non-biting
midges (Chironomidae) (p.273).
12.1.1 The Chemical Nature of Free Amino
Acids
As the biosynthesis of cell proteins requires 20
standard amino acids, these must all be present in
the pool of free amino acids. Previous publications about certain organisms or tissues in which
fewer amino acids were typically found were
based upon the insufficiently sensitive methods of
paper and thin-layer chromatography. In addition
to the standard amino acids, the pool of small nit-