Amino acids basicity

The amino acids, basic building blocks of proteins, all share this dual acid-base character. See Chapter 13 for a description of the amino acids and their biological chemistry. Organic bases also have a long and varied history as painkillers and narcotics, as our Chemishy and Life Box on the next page describes. 

In the human CNS, glutamate is the most important excitatory neurotransmitter. Glycine is a major inhibitory neurotransmitter in the human CNS. Thus, these two amino acids, basic constituents of proteins, also function in other very important ways in behavior, emotion, learning, memory, and sensory perception. Nature uses its molecular constructs for more than one purpose. Among other neurotransmitters, dopamine, epinephrine, norepinephrine, and serotonin are derivatives of protein amino acids and are synthesized from them. 

Name and source Ring bond amino acid Intermediate amino acid Basic end amino acid Molecular formula MW mp Md6 Refs.0... 

Name and source R Amino acid Basic end methylation degree Molecular formula MW mp Wd Ref. 

Among amino acids some L-amino acids are known to be bitter ones. Aromatic amino acids, basic amino acids, and branched-chain amino acids are bitter amino acids. Several bitter amino acids are essential for humans. 

Amino acids Basic Pd-complex Acid Complexes Cations [92,93]... 

About 70% of the filtered Na and K is resorbed in the proximal tubule. Sodium is cotransported with glucose and the amino adds, resulting in the resorption of over 99% of these nutrients. Cotransport of Na with bicarbonate results in resorption of 80 to 90% of the filtered bicarbonate. The uptake of these nutrients at the apical membrane occurs by Na mino acid and Na-glucose cotransport systems. One of two sodium ions are cotransported with each glucose. Seven Na-amino acid cotransport systems have been found in the renal tubule. These include systems specific for acidic amino acids, basic amino acids, glycine, neutral amino acids, cysteine, and cystine. One or more sodium ions are cotransported with each amino acid. 

Jager, P. L., Vaalburg, W., Pruim, J., et al. (2001) Radiolabeled amino acids Basic aspects and clinical applications in oncology. Journal of Nuclear Medicine, 42(3), 432-445. 

Free amino acids are transported into enterocytes by four active, carrier-mediated, Na+-dependent transport systems remarkably similar to the system for glucose. These systems transport, respectively, neutral amino acids basic amino acids (Lys, Arg, His) and cystine aspartic and glutamic acids and glycine and imino acids. Some amino acids (e.g., glycine) have affinities for more... 

Intracellular metabolism of amino acids requires their transport across the cell membrane. Transport of L-amino acids occurs against a concentration gradient and is an active process usually coupled to Na -dependent carrier systems as for transport of glucose across the intestinal mucosa (Chapter 12). At least five transport systems for amino acids (with overlapping specificities) have been identified in kidney and intestine. They transport neutral amino acids, acidic amino acids, basic amino acids, ornithine and cystine, and glycine and proline, respectively. Within a given carrier system, amino acids may compete for transport (e.g., phenylalanine with tryptophan). Na+-independent transport carriers for neutral and lipophilic amino acids have also been described, d-Amino acids are transported by simple diffusion favored by a concentration gradient. 

Produced by the Wax Rose sea anemone (Ammonia sulcata). 47 amino acid basic polypeptide, MW 4770. Prolongs opening of voltage-gated Na+ channels. Reports of human deaths due to exposure in the Mediterranean. 

A large number of toxic peptides are found in cone snails (Conidae). They include four classes of small (13-29 amino acid) basic peptides, known as conotoxins, that have paralytic effects cu-conotoxins block presynaptic calcium channels, a-conotoxins bind to nicotinic ACh receptors in muscle, p-contoxins bind to muscle sodium channels, K-conotoxins may affect potassium channels. Other cone snail toxins include sleeper that induces sleep in mice, conopressin that produces scratching behaviour in mice and increases blood pressure in mammals and a larger (ca. 100 amino acid) toxin that produces convulsions in mice. 

Acidic Amino Acids Basic Amino Acids ... 

By comparing the amino acids basicities, the relative rate at which they will move up a column, may be determined. The amino acids to be separated are ... 

Amino acids with hydroxyl or sulfur-containing side chains Aromatic amino acids Cyclic amino acids Basic amino acids... 

As indicated in Fig. 1 the two-dimensional area is divided into parts for acidic amino acids, neutral amino acids, basic amino acids and amines. This simple rule holds true not only for the protein amino acids but for a large number of nonprotein amino acids. 

This same full-scan and SRM approach used for ACs is also done for amino acids. Basic amino acids such as citrulline and arginine are characterized by loss of 102 Da and ammonia or other basic amino side chain. Selective reaction monitoring (SRM) is used rather than full scan and is based on NL of 119 for citrulline (102 -I-17, where 17 is ammonia) and NL of 161 for arginine (102 -i- 59, where 59 is the amino side chain). These SRMs are often grouped together in the visual spectrum as shown in Figure 13.12. Note that citrulline can also be acquired in an NL 102 scan since source-induced dissociate may cause the ammonia to be lost and hence detection of m/z 215 (MH+ minus 17) versus m/z 232. Details of this fragmentation are described elsewhere. 

The scientists purifying the iron enzyme that takes nitrogen groups off adenine nucleotides found that it had a double life. When they purified it in the lab, its activity was dead because its iron had reacted oxygen with nitrogen- and suUur-containing amino acids. Basically, it acted as a catalase on itself. 

Jager PL, Vaalburg W, Pruim J, de Vries EG, Langen KJ, Piers DA. Radiolabeled amino acids basic aspects and cUnical applications in oncology. J Nucl Med 2001 42 432-445. 

Since the beginning, NCL has undergone a rapid evolution. Up to now, several strategies have been developed to apply NCL to proteins, which do not contain any cysteine residues or cysteines at unfavorable sites (Fig. 2). The first attempts toward cysteine-ffee ligations were made by Tam et al. who chose an N-terminal histidine as acyl acceptor during the ligation, however, with moderate success [5]. Selenocysteine, the 21st natural amino acid, basically reacts the same way as cysteine but exhibits increased nucleophilicity that leads to accelerated reaction rates [6]. 

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