Natural Poly Amino Acids

There are several differences between the proteins and the poly(amino acids) (i) protein is composed of a variety of amino acids, whereas a poly(amino acid) consists of only one type of amino acid, at least in the backbone, (ii) Protein is 

CGP seems to be a compound whose distribution is limited to cyanobacteria [312]. 

No ultrastructural evidence exists so far for the occurrence of similar inclusions in other organisms, and as such it is not possible to identify material with the typical characteristics of cyanophycin from other sources. The granules made of cyanophycin vary in size and shape [313, 314] and occur in aU cyanobacterial groups unicellular and filamentous, nitrogen-fixing, and non-nitrogen-fbdng. Cyanophycin 

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Several other polyamides are derived from natural poly(amino acids) that are subject to a subsequent synthetic treatment. Examples are casein, groundnut protein fiber, and zein, which after a treatment with formaldehyde led to new materials with better mechanical/solubility properties. For example, casein is a mixture of several proteins that forms 3% of milk (as casein calcium salt). Casein can be fractionated into simpler proteins designated as a, 3, y, and k [37]. The amino acid content of casein is similar to... 

Natural poly (amino acids) are ionic polymers having only one type of amino acid joined together with amide linkages. When used as a biomaterial, polyfy-glutamic acid) (yPGA) and poly(L-lysine) are the two most commonly studied natural poly(amino acids). 

Unfortunately, the modification of the side chain is not a generally applicable approach. Among the major, naturally occurring amino acids, only L-lysine has a chemically reactive side chain that would be as readily available for chemical modification as the side chain of glutamic or aspartic acid. Since, however, poly (L-lysine) is known to be toxic (10), its derivatives cannot be candidates for generally applicable biomaterials. Thus, most of the poly(amino acids) that have so far been suggested as biomaterials are derivatives of gluteunic or aspartic acid or copolymers of such derivatives with leucine, methionine, or a limited number of additional amino acids (11). 

Whereas conventional poly (amino acids) are probably best grouped together with proteins, polysaccharides, and other endogenous polymeric materials, the pseudopoly (amino acids) can no longer be regarded as "natural polymers." Rather, they are synthetic polymers derived from natural metabolites (e.g., a-L-amino acids) as monomers. In this sense, pseudopoly (amino acids) are similar to polylactic acid, which is also a synthetic polymer, derived exclusively from a natural metabolite. 

Many polymers have been studied for their usefulness in producing pharmacologically active complexes with proteins or drugs. Synthetic and natural polymers such as polysaccharides, poly(L-lysine) and other poly(amino acids), poly(vinyl alcohols), polyvinylpyrrolidinones, poly(acrylic acid) derivatives, various polyurethanes, and polyphosphazenes have been coupled to with a diversity of substances to explore their properties (Duncan and Kopecek, 1984 Braatz et al., 1993). Copolymer preparations of two monomers also have been tried (Nathan et al., 1993). 

Macromolecules as drug carriers may be divided into degradable and nondegradable types based on their fate within the organism. Biodegradable polymeric drug carriers are traditionally derived from natural products polysaccharides, poly(amino acids) in the hope that the body s natural catabolic mechanisms will act to break down the macromolecular structure into small,... 

The poly (amino acid)s with aromatic side chains behave somewhat differently. In poly(phenylalanine) the a-carbon radical is the major radical species observed, but radicals formed by hydrogen atom addition to the ring are also found. Benzyl radicals formed by side-chain cleavage are present, but only in very low yield. In poly (tyrosine) the only radical species observed is the tyrosyl phenoxyl radical formed by loss of the hydroxyl hydrogen. There is no evidence for formation of significant concentrations of a-carbon radicals. Thus, the nature of the substituents can strongly influence the radiation sensitivity of the backbone chain. 

N 036 Helix-Coil Stability Constants for the Naturally Occurring Amino Acids in Water. III. Glycine Parameters from Random Poly(hydroxybutylglutamine-co-glycine)"... 

From the viewpoint of polylactic acid and polyglycolic acid, byproducts of which are chemicals naturally present in body, the development of poly(amino acids) is genuine. However, the antigenic nature of the poly(amino acids) that contain three or more amino acids inhibits their widespread use. Besides, the cleavage of the amide bond depends on enzymes, resulting in poor in vivo controlled release. Poly(amino acids) have been used mainly to deliver drugs from implants in animals. 

Compound A is a novel poly(ester amide) copolymer that can be used as a bioabsorbable coating for the controlled release of drugs. A is a copolymer of four monomers, two of which are amino acids or amino acid derivatives The body s enzymes recognize the naturally occurring amino acids in the polymer backbone, allowing for controlled enzymatic breakdown of the polymer and steady release of an encapsulated drug. Identify the four monomers used to synthesize A then use Figure 28.2 to name the two amino acids. 

Polymers of the naturally occurring amino acids alanine, leucine, and methionine all show interactions which depend on the relative directions of the backbones. In contrast, poly(L-norleucine) shows less specific interactions clearly for the hydrophobic regions of proteins to function in a precise manner the natural amino acids are most suitable. 

The third mechanism is represented by nonmodular one-step peptide synthesis. Enzymes belonging to this group catalyze the biosynthesis of poly(amino acids). Naturally occurring poly(amino acids) comprise cyanophy-cin [multi-L-arginyl-poly-(L-aspartic acid) cyanophycin granule polypeptide, (CGP)], (poly-(e-lysine) (PL), and poly-(y-glutamate) (PGA). As a consequence of non-ribosomal biosynthesis these peptides reveal a polydisperse mass distribution. 

Sueki, M., Lee, S., Powers, S. R, Denton, J. B., Konishi, Y , Scheraga, H. A. (1984). Helix-coil stability constants for the naturally occurring amino acids in water. 22. Histidine parameters from rsmdom poly[(hydroxybutyl)glutamine-co-L-histidine],... 

Among the three different poly(amino acids), poly(glutamic acid) (PGA) is the most abundant and widely used. The reasons for its wide applications can be attributed to its safety profile, degradability to nontoxic components, and its edibility. PGA has been obtained in nature as well as can be synthesized in several ways. Some of the most common natural and synthetic pathways have been discussed in the succeeding text. 

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