Side-chain composition

Gel permeation chromatography of protein linear random coils in guanidinium chloride allows simultaneous resolution and molecular weight analysis of polypeptide components. Column calibration results are expressed in terms of a log M vs. Kd plot or of effective hydrodynamic radius (Re/). For linear polypeptide random coils in 6M GuHCl, Re is proportional to M0 555, and M° 555 or Re may be used interchangeably. Similarly, calibration data may be interpreted in terms of N° 555 (N is the number of amino acid residues in the polypeptide chain), probably the most appropriate calibration term provided sequence data are available for standards. Re for randomly coiled peptide heteropolymers is insensitive to amino acid residue side-chain composition, permitting incorporation of chromophoric, radioactive, and fluorescent substituents to enhance detection sensitivity. 

In a chemical enzyme-modification experiment conducted by E. F. Jansen and colleagues in 1949, chymotrypsin was incubated with 32P-Iabeled DFP and then hydrolyzed with a strong acid. Separation of the constituent amino acids revealed 1 mol of labeled Ophosphorylserine per 25,000 g of chymotrypsin. Since DFP is a potent inhibitor of the enzyme chymotrypsin, what might we infer about the amino acid side-chain composition of the active site ... 

It might be expected that amide and backbone bands in the spectra of a-(Ala) would be representative of frequencies to be found in all a-helical polypeptides. Evidence has suggested, however, that the amide-III frequencies are sensitive to side-chain composition (Hsu et al., 1976). It is, therefore, important that a detailed analysis of another a-helical polypeptide be available so that the influence of this factor can be assessed. 

Fig. 3.—Variability s of Carbohydrate Side-Chain Composition for Eleven Mucins (Relative to GalNAc).

The presence of non-interacting components in a macromrriecular system of different molecular weight or density, or both. Quasi-continuous distribution of mucin molecular weights arising from variability in carbohydrate side-chain composition. 

Compounds of iron complexed in a porphyrin (tetrapyrrole) ring differ in side chain composition. Haems are the prosthetic groups of cytochromes and are found in most oxygen carrier proteins. 

Side-Chain Composition 10.2.4.1 Homopolymer Side Chains... 

Appendix 3.A1 Name, abbreviations and side-chain composition of the 20 common amino acid residues. 

In the pioneer paper published by Thierry and Skoulios [20], it was advanced that polypeptides with sufficient long polymethylene side chains could display liquid-crystalline phases upon melting of the side chain. They in fact reported a high temperature nematic phase that reversed upon cooling into a lower temperature phase, whose structure was not elucidated. Since then, a good amount of research has been made on comblike polyglutamates, with the focus mainly toward the development of thin films with thermochromic properties. The liquid-crystal structure anticipated for these systems should be cholesteric according to the chiral nature of the main chain a-helix. However other mesomorphs have been described under certain conditions and for certain side chain compositions. 

When this urine was treated with alkali and dithionite a red color was produced. The red pigments, pentdyopents, have an absorption band in the neighborhood of 525 xa.fi] they are salts which autoxidize very readily to colorless forms, and they also become colorless in very weak acids. Pro-pentdyopent was isolated from gall stones as colorless crystals by Fischer and Dobeneck (33a) and was found to consist of two dipyrroles, differing in side chain composition, and derivable from bilirubin by oxidation. 

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