What Are the Acid-Base Properties of Amino Acids

Although the vast majority of plant and animal proteins are constructed from just these 20 a-amino acids, many other amino acids are also found in nature. Ornithine and citmlline, for example, are found predominantly in the liver and are integral parts of the urea cycle, the metabolic pathway that converts ammonia to urea  

Thyroxine and triiodothyronine, two of several hormones derived from the amino acid tyrosine, are found in thyroid tissue  

The principal function of these two hormones is to stimulate metabolism in other cells and tissues. 

4-Aminobutanoic acid (y-aminobutyric acid, or GABA) is found in high concentration (0.8 mM) in the brain, but in no significant amounts in any other mammalian tissue. GABA is synthesized in neural tissue by decarboxylation of the a-carboxyl group of glutamic acid and is a neurotransmitter in the central nervous system of invertebrates and possibly in humans as well  

Only L-amino acids are found in proteins, and only rarely are D-amino acids a part of the metabolism of higher organisms. Several D-amino acids, however, along with their L-enantiomers, are found in lower forms of life. D-Alanine and D-glutamic acid, for example, are structural components of the cell walls of certain bacteria. Several D-amino acids are also found in peptide antibiotics. 

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What Are the Acid-Base Properties of Amino Acids ... 

The discussion of protein solubility in Chapter 9 leads logically into the next topic because it is usually necessary to have proteins in solution in order to characterize them. Of course, some important characterization can be made by hydrolyzing the proteins (e.g., determination of the amino acid composition and sequence). What we are mainly concerned with in this chapter is the measurement of molecular composition and properties of proteins or their subimits in or close to their native state. This is required if our aim is to relate composition to fimctional properties. The classification of cereal proteins into four groups based on solubility was described in the previous chapter. This classification still proves to be valuable for researchers. However, in recent times, techniques have been developed that enable more accurate quantification of cereal protein composition. 

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