FTIR microspectroscopic analysis: future perspectives. Bone mineral
Bone mineral is a poorly crystalline hydroxyapatite [Ca5(PO4)3OH] phase. Ion substitutions are abundant. For example, Na+1, and Mg+2 are substituting Ca+2 ions, HPO4-2 ions substituting the phosphate ions, Cl-1 and F-1 substituting OH-1, and CO3-2 substituting for either phosphate or hydroxyl groups. Once mineral is deposited in bone by osteoblasts, it is not a static moiety, but rather a dynamic one. Since it is bathed in aqueous biological fluids, the type and extent of these substitutions changes with time resulting in alterations of the mineral maturity, which is accompanied by changes in mineral crystallite size and /or shape.
The contribution of mineral maturity, and crystallite size and shape to bone strength is very apparent in the case of fluoride treated bone.
In both animal models and in humans it has been reported that osteoporotic bone mineral characteristically consists of crystals which are larger and more perfect than in normal bone, smaller and less perfect, or that there are no differences. Typically in these studies, tissues were homogenized prior to analysis, concealing the effect of spatial variations in mineral properties. Recently, utilizing techniques such as Small Angle X-ray Scattering (SAXS), and quantitative backscattered electron imaging (qBEI), the analysis of bone mineral (poorly crystalline hydroxyapatite) at the microscopic level and the contribution of mineral crystallinity (crystallite size) and maturity (chemical composition) to bone strength is being actively pursued. Based on such studies, models for the importance of mineral crystallite shape and size in determining bone strength have been put forth.
Bone collagen & collagen cross-links
The organic matrix of bone consists of collagen and a series of non-collagenous proteins and lipids. Some 85%-90% of the total bone protein consists of collagen fibers. Type I collagen, the principal component of the organic matrix of bone, as well as other connective tissues, is a large fibrous protein with a highly repetitive amino acid sequence [Gly (glycine) – X – Y]n (often X is proline and Y is hydroxyproline). This repetitive sequence allows three polypeptide chains (called a chains; type I collagen is composed of two a1 and one a2 chains) to fold into a unique triple-helical structure. It consists of three domains: the —NH2 terminal nontriple helical, the triple helical, and the —COOH terminal nontriple helical domains. The single uninterrupted triple helical domain represents more than 95% of the molecule.
The most distinct feature of type I collagen in mineralized tissues can be seen in its cross-linking chemistry and molecular packing structure. The intermolecular cross-linking provides the fibrillar matrices with various mechanical properties such as tensile strength and viscoelasticity. All the known cross-links of type I collagen are condensation products between the prosthetic groups of juxtaposed specific peptidyl residues of lysine (Lys), hydroxylysine (Hyl), and histidine (His). At present, seven major collagen cross-links have been established as naturally occurring intermolecular cross-links. They are dehydrodihydroxylysinonorleucine (deH-DHLNL), dehydrohydroxylysinonorleucine (deH-HLNL), dehydro- histidinohydroxymerodesmosine (deH-HHMD), pyridinoline (Pyr), deoxypyridinoline (d-Pyr; lysyl analog of Pyr), pyrrole, and histidinohydroxylysinonorleucine (HHL). The first three are NaBH4-reducible (their reduced forms are referred to as DHLNL, HLNL, and HHMD, respectively) and the rest are non-reducible compounds.
Altered collagen structure and inferior bone mechanical properties are encountered in the case of osteogenesis imperfecta, in both humans and animal models. The importance of collagen intermolecular cross-links to the mechanical performance of bone is also very apparent in the pyridoxine deficient chick animal model, as well as in lathyrism.
You can get all the drugs you want for treating your problem in no time if you order it at the cialis professional. We are recommending this pharmacy with confidence because it already has thousands of satisfied customers.