Amino acids structure, chemistry

This chapter will cover the synthetic, structural, and solution chemistry of rare earth complexes with carboxylic acids, polyaminopolycarboxylic acids, and amino acids, with an emphasis on their structural chemistry. As the carboxylate groups play the key roles in the metal-ligand coordination bonding in these complexes, we will start the chapter with the coordination chemistry of rare earth-carboxylic acid complexes, followed by rare earth-polyaminopolycarboxylic acid and rare earth-amino acid coordination chemistry. Owing to length limitations, an exhaustive citation of the large amount of research activities on the subjects is not possible. Instead, only selected examples are detailed to highlight the key features of this chemistry. 

The relationship between structure and function reaches its ultimate expression in the chemistry of amino acids, peptides, and proteins. 

As in most aspects of chemistry and biochemistry, structure is the key to function. We ll explore the structure of proteins by first concentrating on their fundamental building block units, the a-amino acids. Then, after developing the principles of peptide str-ucture, we ll see how the insights gained from these smaller molecules aid our understanding of proteins. 

The structure of the UQ-cyt c reductase, also known as the cytochrome bc complex, has been determined by Johann Deisenhofer and his colleagues. (Deisenhofer was a co-recipient of the Nobel Prize in Chemistry for his work on the structure of a photosynthetic reaction center [see Chapter 22]). The complex is a dimer, with each monomer consisting of 11 protein subunits and 2165 amino acid residues (monomer mass, 248 kD). The dimeric structure is pear-shaped and consists of a large domain that extends 75 A into the mito-... 

Continuing our look at the four main classes of biomolecules, we ll focus in this chapter on amino acids, the fundamental building blocks from which the 100,000 or so proteins in our bodies are made. We ll then see how amino acids are incorporated into proteins and the structures of those proteins. Any understanding of biological chemistry would be impossible without this study. 

William Howard Stein fl 911-1980) was born in New York City and received his Ph.D. in 1938 from the Columbia College of Physicians and Surgeons. He immediately joined the faculty of the Rockefeller Institute, where he remained until his death. In 1972, he shared the Nobel Prize in chemistry for his work with Stanford Moore on developing methods of amino acid analysis and for determining the structure of ribonuclease. 

These steps can be repeated to add one amino acid at a time to the growing chain or to link two peptide chains together. Many remarkable achievements in peptide synthesis have been reported, including a complete synthesis of human insulin. Insulin is composed of two chains totaling 51 amino acids linked by two disulfide bridges. Its structure was determined by Frederick Sanger, who received the 1958 Nobel Prize in chemistry for his work. 

Protein (Section 26.4) A large peptide containing 50 or more amino acid residues. Proteins serve both as structural materials and as enzymes that control an organism s chemistry. 

West, K.A. and Crabb, J.W 1990 Performance evaluation automatic hydrolysis and PTC amino acid analysis. In Vallafraca, J.J., ed.. Current Research in Protein Chemistry Techniques, Structure, and Function. San Diego, Academic Press 37-48. 

In peptide chemistry, the term "pseudopeptide" is commonly used to denote a peptide in which some or all of the amino acids are linked together by bonds other than the conventional peptide Linkage (13). Such pseudopeptides have found applications as specific structural... 

It is not only the activity that can be altered by incorporation of noncoded amino acids. Introduction of structures possessing certain chemical functions leads to the possibility of highly regioselective modification of enzymes. For example, selective enzymatic modification of cystein residues with compounds containing azide groups has led to the preparation of enzymes that could be selectively immobilized using click chemistry methods [99]. 

Biocatalysis refers to catalysis by enzymes. The enzyme may be introduced into the reaction in a purified isolated form or as a whole-cell micro-organism. Enzymes are highly complex proteins, typically made up of 100 to 400 amino acid units. The catalytic properties of an enzyme depend on the actual sequence of amino acids, which also determines its three-dimensional structure. In this respect the location of cysteine groups is particularly important since these form stable disulfide linkages, which hold the structure in place. This three-dimensional structure, whilst not directly involved in the catalysis, plays an important role by holding the active site or sites on the enzyme in the correct orientation to act as a catalyst. Some important aspects of enzyme catalysis, relevant to green chemistry, are summarized in Table 4.3. 

With the death of the bean, cellular structure is lost, allowing the mixing of water-soluble components that normally would not come into contact with each other. The complex chemistry that occurs during fermentation is not fully understood, but certain cocoa enzymes such as glycosidase, protease, and polyphenol oxidase are active. In general, proteins are hydrolyzed to smaller proteins and amino acids, complex glycosides are split, polyphenols are partially transformed, sugars are hydrolyzed, volatile acids are formed, and purine alkaloids diffuse into the bean shell. The chemical composition of both unfermented and fermented cocoa beans is compared in Table 1. 

---