Biological functions of natural and

Biological functions of natural and synthetic bioactive heterocycles... 

Biological Functions of Natural and Synthetic Bioactive Fleterocycles... 

Synthetic porphyrins have been used extensively as model systems for investigating the complex biological functions of natural porphyrin-containing systems. Given the capabilities of porphyrins to bind and release gases and to act as the active center in catalytic reactions in biological systems, porphyrin-... 

The biological function of peptides and proteins depends on their native conformation. The side-chain functionalities of the a-amino acids that comprise peptides and proteins have profound effects on their properties. These functionalities reside in the 20 naturally occurring a-amino acids, which have different propensities for formation of the three major secondary structural conformations. 1 In addition to these naturally occurring a-amino acids whose primary structure enables the polypeptide to fold into a predictable secondary and tertiary structure, the incorporation of unnatural amino acids has opened important areas of research. 

The number of new natural products containing pyrroles and their benzo derivatives has increased considerably during the past decade. Due to space restrictions, only the most representative examples are included, and these witness the variety of structures and biological functions of natural products containing pyrroles, indoles, carbazoles, and related skeletons. 

The chemistry and biological function of natural marine toxins. ChemRec 1, 228-242. 

For a review on the isolation and structure elucidation of the marine polyethers Yasumoto T. The chemistry and biological function of natural marine toxins. Chem. Rec. 2001 1 228-242. 

Synthetic polysaccharides are prepared mainly to obtain models which may be helpful in establishing the biological functions of natural polysaccharides. It is desirable to find systems in which the polymerization of anhydro sugars proceeds stereospecifi-cally, i.e. to prepare uniform and well defined structures. 

In this work, the solutions of human serum albumin (HSA) (>96%, Sigma) and of bovine serum albumin (BSA) (>98%, MP Biomedicals) in a phosphate buffer (0.01 M, pH 7.4) have been used. The proteins concentrations were lO- (absorption spectra measurement) and 10- M (fluorescence measurement at the nanosecond laser fluorimeter). All of the experiments were performed at a temperature of 25 1 °C. The structure and biological functions of HSA and BSA can be found in (Peters, 1996). Tryptophan, tyrosine, and phenylalanine (with relative contents of 1 18 31 in HSA and 2 20 27 in BSA) are the absorption groups in these proteins (as in many other natural proteins). The tyrosine fluorescence in HSA and BSA (as in many other natural proteins) is quenched due to the effect of adjacent peptide bonds, polar groups (such as CO, NH2), and other factors, and phenylalanine has a low fluorescence quantum yield (0.03) (Permyakov, 1992). Therefore, the fluorescence signal in these proteins is determined mainly by tryptophan groups. In that case the fluorescence, registered in nonlinear and kinetic laser fluorimetry measurements, correspond to tryptophan residues (this fact will be used in Section 6.1). 

Most reports concerning 2//-pyran-2-ones (a-pyrones) involve non-fluorinated derivatives, which perform important biological functions in nature and have unlimited synthetic potential for the construction of a variety of arenes and heteroarenes [28], However, very few deal with 2-pyrones containing fluoroalkyl groups. It is evident that the C-2, C-4 and C-6 positions of the 2-pyranone ring are electrophilic in nature and prone to nucleophilic attack. The presence of polyfluoroalkyl substituents on the pyrone ring favours these reactions. At the same time, R -containing 2-pyrones behave as cyclic dienes in cycloadditions. 

About the same time, a new international research journal, Carbohydrate Research, appeared (volume 1) in 1964. It has become the principal journal for the publication of all aspects of carbohydrate research, such as chemical synthesis and modification enzymatic synthesis organic and enzymatic mechanisms involving carbohydrates carbohydrate metabolism conformational analysis isolation of carbohydrates from natural sources analytical methods chemistry of monosaccharides, oligosaccharides, and polysaccharides biological function of carbohydrates and physical properties. Approximately four to five volumes are published each year. 

Sulfenyl halides have so far been used in studies on the role of tryptophan in biological function of enzymes and also for the analytical determination of this amino acid. Looking beyond its use on problems connected with enzymology and protein chemistry, since the sulfenylation reaction is generally valid the ubiquity of the indole nucleus will prompt its application to other naturally occurring indole substances. 

Irrespective of the development of media, many of the traditional media are successfully defending their position. This is due to their hydrophilic nature, preserving biological function of the separated molecules, but also the fact that columns may be prepared easily and, finally, some of the classical media, e.g., Sephadex, have a selectivity that is so far unsurpassed and therefore very fit for use. Intersting enough, Sephadex is still the premiere gel filtration medium for desalting due to the optimal pore size and particle size of this medium (see Section II,C). 

Granhall, U. (1981). Biological nitrogen fixation in relation to environmental factors and functioning of natural ecosystems. In "Terrestrial Nitrogen Cycles" (F. E. Clark and T. Rosswall, eds). Ecological Bulletin 33, 131-145. Swedish Natural Science Research Council, Stockholm. 

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