Protein precipitation description

A review of efforts to experimentally characterize and model the phenomena important in protein precipitation shows that, despite successes, continued work is necessary to produce accurate mechanistic descriptions of this method of protein recovery. 

Mineralization is the precipitation of calcium phosphate, but biochemical mediation of this process is not fully understood. In this chapter, the chemistry underlying mineralization (Sect. 1) and the structures ofbones and teeth (Sect. 2) are described. Osteoblasts secrete osteoid matrix and matrix vesicles that transport type I collagen and calcium phosphate, respectively, to the matrix where they will mineralize. Secreted matrix vesicles take up calcium and phosphate until they burst and release the calcium phosphate, which then redissolves and remineralizes around the type I collagen (Sect. 3). Glycoproteins involved in correctly modeling bone and dentin, and the role of osteocalcin in limiting excessive bone growth is then discussed (Sect. 4). There follows a detailed description of enamel (E) mineralization and of the major proteins involved (Sect. 5) followed by two summaries the difference between enamel and bone mineralization, and the vitamins required for mineralization (Sect. 6). 

A true tannin is operationally defined as a substance that will precipitate proteins from aqueous solutions. The pentagallate will not fit this description but a nonagallate will. 

Present knowledge of the details of the conformation of proteins is based almost exclusively on results of studies of protein crystals by x-ray diffraction. Protein crystals contain anywhere from 20 to 80% solvent (1 ) (dilute buffer, often containing a high molarity of salt or organic precipitant). While some solvent molecules can be discerned as discrete maxima of the electron density distribution calculated from the x-ray results, the majority of the solvent molecules cannot be located in this manner most of the solvent appears to be very mobile and to have a fluctuating structure perhaps similar to that of liquid water. Many additional distinct locations near which a solvent molecule is present during much of the time have been identified in the course of crystallographic refinement of several small proteins (2,3,4,5, 6), but in all cases the description of solvent structure in the crystal is incomplete probably because only a statistical description is inherently appropriate. 

The description of a phenotype can lead to the prediction that a viral protein directly complexes with a specific cellular protein. An antibody against the cellular target protein can then be used to co-precipitate viral proteins with the cellular protein from virus-infected cells. 

One of the early qualitative tests to determine whether or not a substance was an orthophosphate or a condensed phosphate was to mix the phosphate in question with a protein such as egg albumin. If the phosphate reacted with the protein and precipitated, it was likely the phosphate was a condensed phosphate. The text was not foolproof, but was a good indicator. Many polyelectrolytes precipitate proteins. If one knows that the substance under test is a phosphate of some description, then this narrows the room for error. 

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