Biological and structural significance

Reviews of hydroxyapatite and other calcium orthophosphates including their inorganic and organic occurrences in nature, structure, transformations and biological and biomedical significance have been provided by Dorozhkin (2007) and Heimann (2010a). 

Structural biology has become an exceptionally important field of research since 2005, when the heterologous expression of pathway enzymes in E. coli could be routinely applied. The fold-families, overall 3D molecular structures, substrate and coenzyme binding pockets of six crystallized major enzymes were described. Identification of the catalytic and structurally significant amino acids allowed for the description of enzyme mechanisms and gave reliable guidance for enzyme rational reengineering to deliver novel enzyme mutants with expanded substrate acceptance. 

The availability of water, i.e. the water activity, in a material is of great importance for its biological and biochemical properties. It depends both on the water content, and significantly on the nature of the structural bond of water molecules, in other words, how strongly they are retained by the matrix. Thus, for similar water contents, when determined by Karl Fischer titration, quite different water activities may be obtained for different materials. This is of paramount importance for RM stability. 

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. 

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