5 α-Amino Acids In Water: A Review of VCD and ROA Spectra
85
the vibrational Circular dichroism and Raman optical Activity spectra of amino
acids in water have been intensively studied for alanine, but less so for proline. For
the other amino acids, there are usually a few papers devoted to their experimental
and/or theoretical vibrational chiroptical spectra. Articles comparing the spectra of
more than two amino acids are sparse, as this is usually done at the very beginning
of the application of chiroptical spectra to the analysis of biomolecules. For eight
amino acids, their vCd and RoA spectra were practically unknown. however, at
the beginning of 2012, the number of not-yet-studied amino acids was greater by
four compounds. For the studied amino acids, we report on experimental methods
and techniques as well as tricks for measuring and simulating the vCd and RoA
spectra in water at different ph levels.
the review is concluded by listing the not-yet-measured amino acids, a presentation of the main challenges for computational methods, and suggestions for
the most promising experimental techniques that may be used in future studies on
amino acids in aqueous media.
5.2 Role of Free Amino Acids in an Organism
In humans, the basic set of 20 α-amino acids is categorised into two subgroups: essential and non-essential. the nine essential amino acids cannot be formed in the
human body, which is why they have to be ingested with food to maintain the proper
function of the organism. on the other hand, there are 11 non-essential amino acids
which are synthesised in a simple way from intermediates of the citric acid cycle
and other major pathways. the entire set of proteinogenic amino acids can be synthesised by most microorganisms and plants. the biosynthetic routes of most amino
acids are greatly interrelated with each other in a high-dimensional network, and
also linked to their metabolism and other biochemical processes. there are four
metabolic sources of free amino acids:
1. breakdown of ingested proteins
2. breakdown of cellular proteins
3. breakdown of extra-cellular proteins
4. amino acid biosynthesis
5.2.1 Metabolism
the first step of amino acid metabolism is deamination [3]. the -Nh 2 group can
be transferred onto an acceptor α-ketoacid, which causes the formation of alanine,
aspartate, or glutamate. Aspartate enters the urea cycle, while glutamate is easily
liberated by oxidative deamination of its amino group in the form of ammonia that
also is subject to the same cycle. on the other hand, alanine is an ammonium carrier
from the muscles to the liver (glucose-alanine cycle) [4, 5].
the catabolism of amino acid hydrocarbon skeletons can result in the formation of oxaloacetate, a principal metabolite in gluconeogenesis [6, 7]. this is the
85
the vibrational Circular dichroism and Raman optical Activity spectra of amino
acids in water have been intensively studied for alanine, but less so for proline. For
the other amino acids, there are usually a few papers devoted to their experimental
and/or theoretical vibrational chiroptical spectra. Articles comparing the spectra of
more than two amino acids are sparse, as this is usually done at the very beginning
of the application of chiroptical spectra to the analysis of biomolecules. For eight
amino acids, their vCd and RoA spectra were practically unknown. however, at
the beginning of 2012, the number of not-yet-studied amino acids was greater by
four compounds. For the studied amino acids, we report on experimental methods
and techniques as well as tricks for measuring and simulating the vCd and RoA
spectra in water at different ph levels.
the review is concluded by listing the not-yet-measured amino acids, a presentation of the main challenges for computational methods, and suggestions for
the most promising experimental techniques that may be used in future studies on
amino acids in aqueous media.
5.2 Role of Free Amino Acids in an Organism
In humans, the basic set of 20 α-amino acids is categorised into two subgroups: essential and non-essential. the nine essential amino acids cannot be formed in the
human body, which is why they have to be ingested with food to maintain the proper
function of the organism. on the other hand, there are 11 non-essential amino acids
which are synthesised in a simple way from intermediates of the citric acid cycle
and other major pathways. the entire set of proteinogenic amino acids can be synthesised by most microorganisms and plants. the biosynthetic routes of most amino
acids are greatly interrelated with each other in a high-dimensional network, and
also linked to their metabolism and other biochemical processes. there are four
metabolic sources of free amino acids:
1. breakdown of ingested proteins
2. breakdown of cellular proteins
3. breakdown of extra-cellular proteins
4. amino acid biosynthesis
5.2.1 Metabolism
the first step of amino acid metabolism is deamination [3]. the -Nh 2 group can
be transferred onto an acceptor α-ketoacid, which causes the formation of alanine,
aspartate, or glutamate. Aspartate enters the urea cycle, while glutamate is easily
liberated by oxidative deamination of its amino group in the form of ammonia that
also is subject to the same cycle. on the other hand, alanine is an ammonium carrier
from the muscles to the liver (glucose-alanine cycle) [4, 5].
the catabolism of amino acid hydrocarbon skeletons can result in the formation of oxaloacetate, a principal metabolite in gluconeogenesis [6, 7]. this is the