Complex carbohydrates, biological information

It is important to consider the nature of the desialylation experiment in view of the purity of sialidase preparations. The use of highly purified sialidase can provide additional information related to complex carbohydrate structure and the sialidase specificity while effecting desialylation. This approach also generates sialic acid-free complex carbohydrates for use as e.g. sialyltransferase substrates, or, in biological systems, desialylated cell-surface glycoconjugates. Cruder preparations frequently contain proteinase and other glycosidase activities which will also degrade the material. Furthermore, consideration of the buffer system must include those ions necessary for enzyme activity e.g. V. cholerae sialidase requires approx. 4mM Ca for activity). 

Abstract To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues. 

One of the most important problems that has been actively studied during the past few years is the hydration of biological molecules, especially carbohydrates, and the effect of hydration on the conformation of the solute molecule, as well as the effect of the latter on the water structure. Different theoretical and experimental methods have been utilized, and the discrepancies between the results, expressed as numbers of hydration, are considerable. In addition, the water molecule is a reactant in a number of biochemical reactions. The kinetics of these reactions is influenced both by the conformation of the carbohydrate and the structure of the water. These questions will be discussed, with particular reference to the contribution of the vibrational, spectroscopic information to an understanding of such complex mechanisms. 

A detailed structural study should provide invaluable information concerning the nature of the biologically active groupings of these polysaccharides prior to 1945 no such structural investigations had been carried out. It is probable that the many polysaccharide fractions isolated are constituent parts of one or more main polysaccharide complexes, which have fundamental roles in the immunological behavior of M, tuberculosis. An immense field of work is open to carbohydrate chemists. 

Because they provide so much more information in their n.m.r. spectra, lanthanide complexes have been used, with great success, as probes for the study of biologically important Ca " " complexes. The assumption was made that the complexing site for the two complexes is the same, and the strength of complexing approximately equal. This approach should be applied to uncharged carbohydrates with some caution comparison of the t.l.c. Jif values for Ca " " and La + showed substantial discrepancies, particularly for alditols and glycosides. ... 

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