Protein hydroxyapatite

Substance P Angiotensin II PTH" Basic proteins, Hydroxyapatite, and analysis V2... 

High matrix rigidity is offered by porous sihca, which can be deriva-tized to enhance its compatibility with proteins, but it is unstable at alkaline pH. Hydroxyapatite particles have high selectivity for a wide range of proteins and nucleic acids. 

Fluorid ions stimulate bone formation by a direct mitogenic effect on osteoblasts mediated via protein kinase activation and other pathways. Further to these cellular effects, fluorides alter hydroxyapatite crystals in the bone matrix. In low doses, fluorides induce lamellar bone, while at higher doses abnormal woven bone with inferior quality is formed. The effect of fluorides on normal and abnormal (e.g. osteoporotic) bone therefore depends on the dose administered. 

The cell growth was much faster on the chitosan-hydroxyapatite scaffolds with the glass than on the chitosan-hydroxyapatite scaffold without the glass. The total protein content of cells increased over time on both composites. The cells on the chitosan-hydroxyapatite-glass also expressed significantly higher amount of alkaline phosphatase at days 7 and 11 and osteocalcin at day 7 than those on chitosan-hydroxyapatite [165]. 

Osteocalcin (bone Gla protein) Contains y-carboxyglutamate residues that bind to hydroxyapatite. Bone-specific. 

Osteoclasts are multinucleated cells derived from pluripotent hematopoietic stem cells. Osteoclasts possess an apical membrane domain, exhibiting a ruffled border that plays a key role in bone resorption (Figure 48-12). A proton-translocating ATPase expels protons across the ruffled border into the resorption area, which is the microenvironment of low pH shown in the figure. This lowers the local pH to 4.0 or less, thus increasing the solubility of hydroxyapatite and allowing demineralization to occur. Lysosomal acid proteases are released that digest the now accessible matrix proteins. 

The enzyme was purified to 277 fold with very high specific activity, 1387 unit/mg protein by hydroxyapatite column chromatography (Figure 3). 

The previously proposed uptake models were mathematical assumptions and had no physical or chemical basis. Millard and Hedges, on the other hand, considered the chemistry of bone-uranium interactions. With the D-A model, they proposed that U was diffusing into bone as uranyl complexes, and adsorbing to the large surface area presented by the bone mineral hydroxyapatite (Millard and Hedges 1996). Laboratory experiments showed a partition coefficient between uranyl and hydroxyapatite under oxic conditions of 10" -10, demonstrating U uptake in the U state without the need for reduction by protein decay products as proposed by Rae and Ivanovich (1986). 

Kokubo et al. [16,17] showed that the hydroxyapatite formation on the surfaces of bioactive materials in the living body can be reproduced even in an acellular protein-free simulated body fluid (SB F) with ion concentrations nearly equal to those of human blood plasma. This indicates that the hydroxyapatite layer is formed through chemical reaction of the bioactive glass with the surrounding body fluids. The formed layer consists of carbonated hydroxyapatite with small crystallites and low crystallinity, which is similar to bone hydroxyapatite. Hence the bioactivity of a material can be evaluated even in vitro by examining the hydroxyapatite formation on its surface in SBF. 

SBF is a solution that has inorganic ion concentrations similar to those of human blood plasma but does not contain any cells or protein. A brief summary of SBF, introduced by Cho et al. [17], follows. The ion concentrations of SBF are given in Table 11.1 [17]. The pH of SBF is typically adjusted to 7.25 or 7.40 at 36.5 °C. This fluid is a metastable solution containing calcium and phosphate ions supersaturated with respect to hydroxyapatite. SBF is prepared by successively dissolving the reagent-grade chemicals in ultra-pure water in the order given in Table 11.2 [17]. Each new chemical is added after the previous one has completely dissolved. The temperature... 

Final alcohol precipitation not only allows for removal of the phenol and any remaining non-covalently bound hydrocarbon but also concentrates the DNA. Ribonuclease treatment removes any contaminating RNA. Additional purification by cesium chloride centrifugation (35) is also often performed. This is particularly suited to small quantities of DNA. Hydroxyapatite chromatography is also effective in separating RNA, proteins, and DNA (36.37). 

The first description of calsequestrin (Ref. (80)) gave a significantly higher estimate of 4.4 for logK. Interestingly, some use was made of hydroxyapatite in protein fractionation in this work. 

Hydroxyapatite occurs naturally as a mineral in phosphate rock and also constitutes the mineral portion of bone. It may also be used to fractionate protein by chromatography. 

Dong M, Baggetto LG, Folson P, LeMaire M, Penin F. Complete removal and exchange of sodium dodecyl sulfate bound to soluble and membrane proteins and restoration of their activities, using ceramic hydroxyapatite chromatography. Anal Biochem 1997 247 333-341. 

The nanostructured surfaces resemble, at least to a certain degree, the architecture of physiological adhesion substrates, such as extracellular matrix, which is composed from nanoscale proteins, and in the case of bone, also hydroxyapatite and other inorganic nanocrystals [16,17,24-27]. From this point of view, carbon nanoparticles, such as fullerenes, nanotubes and nanodiamonds, may serve as important novel building blocks for creating artificial bioinspired nanostructured surfaces for bone tissue engineering. 

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