Acid-base chemistry of amino acids

Additional aspects of the acid-base chemistry of amino acids and proteins are considered in Chapter 3, Section A and Chapter 6, Section E. The student may find it appropriate to study these sections at this time and to work the associated study problems. 

Understanding the Acid-Base Chemistry of Amino Acids... 

Evans, C. A., and Rabenstein, D. L. (1974). J. Amer. Chem. Soc. 96, 7312. Nuclear Magnetic Resonance Studies of the Acid-Base Chemistry of Amino Acids and Peptides. II. Dependence of the Acidity of the C-Terminal Carboxyl Group on the Conformation of the C-Terminal Peptide Bond. 

The acid-base chemistry of amino acids is more complicated than shown in Equations 16.48 and 16.49, however. Because the COOH group can act as an acid and the NH2 group can act as a base, amino acids undergo a self-contained Bronsted-Lowry acid-base reaction in which the proton of the carboxyl group is transferred to the basic nitrogen atom ... 

The acid-base chemistry of amino acids and various cofactors are certainly not the only biological structures whose activity depends upon the protonation state. Even DNA responds to pH effects due to acidic and basic sites within its structure. At physiological pH the four heterocyclic bases of nucleotides are neutral, but as the pH is raised, thymine and uridine will undergo deprotonation near pH 10. As the pH is lowered, cytidine will become protonated around pH 6. This protonation has been used to control DNA triple helix formation, as shown in the following Connections highlight. 

This resource describes the classification and chemistry of amino acids, covering the a-amino acids of proteins and their acid-base... 

WE BEGIN THIS CHAPTER with a study of amino acids, compounds whose chemistry is built on amines (Chapter 10) and carboxylic acids (Chapter 13). We concentrate in particular on the acid-base properties of amino acids because these properties are so important in determining many of the properties of proteins, polymers of amino acids that have many functions in living organisms. With this understanding of the chemistry of amino acids, we then examine the structure of proteins themselves. 

The differences in the amino acid chemistry of the hide coUagen and the hair keratin are the basis of the lime-sulfide unhairing system. Hair contains the amino acid cystine. This sulfur-containing amino acid cross-links the polypeptide chains of mature hair proteins. In modem production of bovine leathers the quantity of sulfide, as Na2S or NaSH, is normally 2—4% based on the weight of the hides. The lime is essentially an unhmited supply of alkah buffered to pH 12—12.5. The sulfide breaks the polypeptide S—S cross-links by reduction. Unhairing without sulfide may take several days or weeks. The keratin can be easily hydrolyzed once there is a breakdown in the hair fiber stmcture and the hair can be removed mechanically. The coUagen hydrolysis is not affected by the presence of the sulfides (1—4,7). 

In many cases, the racemization of a substrate required for DKR is difficult As an example, the production of optically pure cc-amino acids, which are used as intermediates for pharmaceuticals, cosmetics, and as chiral synfhons in organic chemistry [31], may be discussed. One of the important methods of the synthesis of amino acids is the hydrolysis of the appropriate hydantoins. Racemic 5-substituted hydantoins 15 are easily available from aldehydes using a commonly known synthetic procedure (Scheme 5.10) [32]. In the next step, they are enantioselectively hydrolyzed by d- or L-specific hydantoinase and the resulting N-carbamoyl amino acids 16 are hydrolyzed to optically pure a-amino acid 17 by other enzymes, namely, L- or D-specific carbamoylase. This process was introduced in the 1970s for the production of L-amino acids 17 [33]. For many substrates, the racemization process is too slow and in order to increase its rate enzymes called racemases are used. In processes the three enzymes, racemase, hydantoinase, and carbamoylase, can be used simultaneously this enables the production of a-amino acids without isolation of intermediates and increases the yield and productivity. Unfortunately, the commercial application of this process is limited because it is based on L-selective hydantoin-hydrolyzing enzymes [34, 35]. For production of D-amino acid the enzymes of opposite stereoselectivity are required. A recent study indicates that the inversion of enantioselectivity of hydantoinase, the key enzyme in the... 

Finding close agreement between the result of a calculation and an established body of empirical data is a delightful experience. To those of us who have witnessed the evolution of the computational tools during their own lifetime, the process has at times appeared like a revolution and a mutation of chemistry (Schafer 1983G, 1991G). The reference section given at the end of this chapter demonstrates that ab initio calculations of amino acids and peptides are at the base of a very active field and have become a powerful source of information on these important molecules. 

In this paper we have tried to present a brief overview of state-of-the-art of the synthetic chemistry of oxide materials based on polybasic carboxylic hydroxy (amino) acid routes. It has been shown that, in spite of enormous number of papers on the subject (we have mentioned just a few latest references, significant efforts should be undertaken in order to... 

In the study of the origin of life on earth, the element carbon is essential. Carbon is a required component of the fundamental molecules of life amino acids, bases, and sugars. In addition, a large variety of carbon compounds is necessary in the complex biochemical cycles of living organisms. The physical and chemical nature and geometry of the carbon atom make it well suited to form the vast array of molecules involved in the chemistry of life. 

The imidazole ring is present in a number of biologically important molecules as exemplified by the amino acid histidine. It can serve as a general base (pA"a = 7.1) or a ligand for various metals (e.g., Zn, etc.) in biological systems. Furthermore, the chemistry of imidazole is prevalent in protein and DNA biomolecules in the form of histidine or adenine/guanine, respectively. 

Schultz and coworkers (Jackson et a ., 1988) have generated an antibody which exhibits behaviour similar to the enzyme chorismate mutase. The enzyme catalyses the conversion of chorismate [49] to prephenate [50] as part of the shikimate pathway for the biosynthesis of aromatic amino acids in plants and micro-organisms (Haslam, 1974 Dixon and Webb, 1979). It is unusual for an enzyme in that it does not seem to employ acid-base chemistry, nucleophilic or electrophilic catalysis, metal ions, or redox chemistry. Rather, it binds the substrate and forces it into the appropriate conformation for reaction and stabilizes the transition state, without using distinct catalytic groups. 

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