Chain properties

Evolution has provided the cell with a repertoire of 20 amino acids to build proteins. The diversity of amino acid side chain properties is enormous, yet many additional functional groups have been selectively chosen to be covalently attached to side chains and this further increases the unique properties of proteins. Diese additional groups play a regulatory role allowing the cell to respond to changing cellular conditions and events. Known covalent modifications of proteins now include phosphorylation, methylation, acetylation, ubi-quitylation, hydroxylation, uridylylation and glycosyl-ation, among many others. Intense study in this field has shown the addition of a phosphate moiety to a protein... 

Viscoelastic and transport properties of polymers in the liquid (solution, melt) or liquid-like (rubber) state determine their processing and application to a large extent and are of basic physical interest [1-3]. An understanding of these dynamic properties at a molecular level, therefore, is of great importance. However, this understanding is complicated by the facts that different motional processes may occur on different length scales and that the dynamics are governed by universal chain properties as well as by the special chemical structure of the monomer units [4, 5],... 

We used this procedure in estimating the chain properties of hyaluronic acid 16). Hyaluronic acid is a regular polysaccharide with a disaccharide repeat unit. The two units are glucuronic acid (Figure 1) and N-acetyl glucosamine (Figure 2). 

Nevertheless, these two worlds are closely related to each other. The typical behaviour of plastics materials, strongly deviating from other materials, can only be understood on the basis of the chain properties. 

Since Tg and Tm are both primarily governed by the same chain properties, namely chain flexibility and chain interactions, some correlation between these two quantities can be expected to be present. In Figure 4.5 Tg and Tm are plotted against each other for a number of polymers. As a first approximation it appears that ... 

The comparison between the two techniques has shown that DPL is more flexible than FDI (any kind of pattern can be transferred on the surface) and less time consuming. On the other hand, very high and large border walls are produced in DPL. The analysis of the properties of these border walls reveals that DPL causes changes in the physical (density) and chemical (length of the chains) properties of the polymer. 

Although the most stimulatory amino acids were identical in the dog (e.g.,L-cysteine, L-proline, L-lysine, L-histidine and L-alanine), interspecies differences could be related to the side chain properties of the amino acids. Thus, amino acids with hydrophobic side chains were normally inactive or inhibitory in the cat, but were often excitatory in the dog. Conversely, amino acids with acidic side chains tended to be somewhat more excitatory in the cat. 

The shapes of the pressure-area isotherms of monolayers of synthetic polypeptides in the a-helical conformation depend on the nature of the side chain interactions. Poly(y-n-decyl-iu-glutamate), poly(i.-leucine), poly(iu-norleucine), and poly(iu-methionine) show differences related to side chain flexibility and dipolar interactions. Comparison of the isotherms of monolayers of the enantiomorphic and racemic forms of polymers [poly(alanine), poly(y-benzyl-glutamate), poly( /3-benzyl-aspartate), poly( e-benzyloxycarbonyllysine )] similarly show features related to side chain properties. The results support the view that when a monolayer consists of a-helices, the shape of the isotherm depends on the difference between the energies of interaction of parallel and antiparallel molecules. These conclusions are discussed in relation to proteins. 

Fig. 3. Alignment of simplified apoLp-IlI sequences. The sequences in Fig. 2 were simplified by grouping amino acids with similar side-chain properties G = G, S, T D = D, E, N, Q H = H, K, R I = A, L, I, M, V, F, Y, W P = P. The asterisks indicate residues with similar side-chain properties found in all four sequences. Species acronyms as in legend to Fig. 2.

M. Muller (1999) Miscibility behavior and single chain properties in polymer blends a bond fluctuation model study. Macromol. Theory Simul. 8, pp. 343-374 M. Muller and K. Binder (1995) Computer-simulation of asymmetric polymer mixtures. Macrrmolecules 28, pp. 1825-1834 ibid. (1994) An algorithm for the semi-grand-canonical simulation of asymmetric polymer mixtures. Computer Phys. Comm. 84, pp. 173-185... 

H. J. Limbach and C. Holm (2003) Single-chain properties of polyelectrolytes in poor solvent. J. Phys. Chem. B 107(32), pp. 8041-8055 H. J. Limbach, C. Holm, and K. Kremer (2002) Structure of polyelectrolytes in poor solvent. Europhys. Lett. 60(4), pp. 566-572... 

Muller M 1999 Misoibility behavior and single chain properties in polymer blends a bond fluctuation model study Maoromol. Theory Simul. 8 343... 

As discussed earlier in Section II, 5, only for typical mammalian collagen is chemical evidence reasonably complete. Table VI adds to the chemical data summarized by Bowes and Kenten (40) several side-chain properties which are useful in considering these appendages in relation to space filling characteristics and ability to scatter X-rays. 

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