Amino acids and simple peptides

A7.4.1 Ions, simple organic compounds, amino acids and simple peptides... 

The interaction of platinum(II) complexes with various amino acids and simple peptides is relevant to understanding the biological fate of platinum anticancer agents such as mplatin, and this area has been reviewed extensively.258-261... 

After direct high-resolution structural measurements on proteins became practicable, interest in crystalline amino acids decreased, but became renewed in attempts to simulate the distribution of electronic charge density in biopolymers using amino acids and simple peptides as model systems, to derive some transferable parameters and potentials [2-15]. Another research direction involved these systems and their packing patterns to mimic selected folds and interaction patterns of biopolymers. Typical molecular conformations and patterns of hydrogen bonds and packing in the structures of crystalline amino acids have been reviewed [16-19]. Similar analyses were performed for small peptides [18, 20-22]. 

Venkatachalam (1968) assumed reasonable values for bond lengths and angles, based on earlier crystal structure results for amino acids and simple peptides, and calculated the possible range of values for and associated with the two corner C atoms in the 4 - 1 bonds of type I and type II. In Figs. 39 and 40 the original range of values is delineated by the solid lines, and the experimentally determined (j) and ij/ values in many crystal structures are plotted. Almost all of the experimental values fall within the predicted range. 

When Robert Corey, an expert in X-ray crystallography, joined Pauling at Caltech, they expanded the experimental work determining the sfiuctures of individual amino acids and simple peptides. The work was interrupted by World War II, but resumed immediately after the war, and Pauling returned to the structure of alpha keratin in 1948 while he was a visiting professor at Oxford University in England. 

Using liposomes made from phospholipids as models of membrane barriers, Chakrabarti and Deamer [417] characterized the permeabilities of several amino acids and simple ions. Phosphate, sodium and potassium ions displayed effective permeabilities 0.1-1.0 x 10 12 cm/s. Hydrophilic amino acids permeated membranes with coefficients 5.1-5.7 x 10 12 cm/s. More lipophilic amino acids indicated values of 250 -10 x 10-12 cm/s. The investigators proposed that the extremely low permeability rates observed for the polar molecules must be controlled by bilayer fluctuations and transient defects, rather than normal partitioning behavior and Born energy barriers. More recently, similar magnitude values of permeabilities were measured for a series of enkephalin peptides [418]. 

We have mentioned before that proteins in foodstuffs are split in the stomach and intestines into amino acids or simple peptides, which pass through the walls into the blood stream, and then may be built up into the special proteins needed by the organism. A process of tearing down the proteins of the body also takes place. For example, red cells have a lifetime of a few weeks at the end of ivhich they are destroyed, beingjeplaced by newly formed red cells. The nitrogen of the protein molecules that are torn down is eliminated in the urine, as urea, CO(NH2)2-... 

Still and coworkers prepared the highly selective, D2-synnnetric receptor 37 for amino acids and small peptides by simple condensation of (/ , )-cyclohexane-1,2-diamihe and trimesic acid. ° Complexes are held together by four intermolecular hydrogen bonds and resemble a peptidic three-strand (1-sheet. A further, enantiomer-discriminating interaction is based on steric complementarity between the amino acid side chain and the cleft-type cavity of the receptor. 

Amino acids and short peptides have played incredibly important roles in the development ofSS NMR spectroscopy. Number of simple, advanced and very sophisticated sequences has been tested employing NAV (N-acetyl-L-Val), NAVL (N-acetyl-L-Val-L-Leu) and MLF (N-formyl-Met-Leu-Phe) peptides as model samples. These methodologies were developed with an intention to apply them further for structural analysis of more complex biological systems as proteins, nucleic acids, etc. Recent achievements in this... 

The distances of the carbonyl carbon to the Cp rings for all structurally characterized Fc-peptides are well within estabhshed bond distances for a normal C-C single bond in Fc-amides [range d(C-C) = 1.43-1.507 A]. Fmthermore, the amide C(0) N group is planar in all Fc-amino acids and Fc-peptides, and the carbonyl C=0 distances compare well wifli simple ferrocene amides. Similarly, the bond distances and angles of the Fc moiety itself are well within established parameters for ferrocene derivatives. ... 

The first point has already been made. It is that the equilibrium position is far over in the direction of hydrolysis. Even in the most favorable case there can be little synthesis from the constituent amino acids by mass action. We are considering the simple case where the amino acids and the peptide are and remain in solution. The case where the peptide formed is relatively insoluble will be discussed later. 

The sequence of amino acids in a peptide can be written using the three-letter code shown in Figure 45.3 or a one-letter code, both in common use. For example, the tripeptide, ala.ala.phe, could be abbreviated further to AAF Although peptides and proteins have chain-like structures, they seldom produce a simple linear system rather, the chains fold and wrap around each other to give complex shapes. The chemical nature of the various amino acid side groups dictates the way in which the chains fold to arrive at a thermodynamically most-favored state. 

Thomson MOW Click Organic Interactive to learn to estimate isoelectric points for simple amino acids and peptides. 

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