Protein structure coagulation

Denaturation is the irreversible precipitation of proteins caused by heating, such as the coagulation of egg white as an egg is cooked, or by addition of strong acids, bases, or other chemicals. This denaturation causes permanent changes in the overall structure of the protein and because of the ease with which proteins are denatured it makes it difficult to study natural protein structure. Nucleic acids also undergo denaturation. 

Fig. 3.10. Modular structure of proteins of coagulation and thrombolysis. The shapes of structural motifs, their amino (N) and carboxyl termini (C) and the stabilizing disulfide bridges (bars) are shown on the top. Shown below each module is the schematic symbol used to represent them in the proteins shown.

A (congenital or acquired) and type 1 von Willebrand disease, in which the VWF protein structure is normal but the plasma concentration is reduced (1). By contrast with conventional coagulation factor concentrates, desmopressin is cheap and is free from the risk of transmission of viral infections, which have proved such a problem in the past. It is also very useful in the treatment of carriers of hemophilia A, many of whom have significant reductions in the baseline concentration of factor VIII. By contrast, desmopressin has no effect on the concentration of factor IX, and is thus of no value in hemophilia B (Christmas disease). It is also of little value in type 2 (abnormal VWF structure) von Willebrand s disease, which accounts for about 15-20% of all cases. The administration of desmopressin to patients with type 2B von Willebrand s disease can be hazardous, as it is likely to cause thrombocytopenia (2). The use of desmopressin in bleeding disorders has been reviewed (3). Tachyphylaxis develops if desmopressin is used for prolonged periods to control bleeding disorders, because desmopressin causes release of stored factor VIII and von Willebrand factor, after which it takes time for them to accumulate again. 

What about the tau protein, the chief component of the tangles, the other pathological trait of Alzheimer s disease In a 1995 study, Olaf Schweers and his colleagues at the Max Planck Unit for Structural Molecular Biology in Hamburg showed that the tau protein only coagulates when... 

Hydrophobic interactions which are enforced (entropy driven) by the nature of water are the principle forces behind protein folding (6). They facilitate the establishment of other stabilizing interactions (7,10). Hydrophobic interactions, being of fundamental importance to protein structure, are very relevant to the functional properties of many food proteins, especially caseins. These forces affect solubility, gelation, coagulation, micelle formation, film formation, surfactant properties and flavor binding (7,10). 

Denaturation is accompanied by changes in both physical and biological properties. Solubility is drastically decreased, as occurs when egg white is cooked and the albumins unfold and coagulate. Most enzymes also lose all catalytic activity when denatured, since a precisely defined tertiary structure is required for their action. Although most denaturation is irreversible, some cases are known where spontaneous renaturation of an unfolded protein to its stable tertiary structure occurs. Renaturation is accompanied by a full recovery of biological activity. 

The six major proteins of milk, asl-, o s2-, and /c-casein, jS-lactoglobulin, and a-lactalbumin, contain at least one tryptophan residue [57], the fluorescence of which allows the monitoring of the structural modifications of proteins and their physicochemical environment during the coagulation processes. Emission fluorescence spectra of the protein tryptophanyl residues were recorded for the milk coagulation kinetics induced by... 

This study has shown that the process used to coagulate milk has a broad effect on fat globule-protein interactions and on the molecular structure of the gel. In addition we have shown that the different molecular structures of the three coagula correspond to different rheological properties. 

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