Insoluble collagen

Scieroproteins. Insoluble proteins obtained from the skeletal and connective tissues of animals. Typical classes are keratins collagens and elastin classes. 

The diversity in primary, secondary, tertiary, and quaternary stmctures of proteins means that few generalisations can be made concerning their chemical properties. Some fulfil stmctural roles, such as the collagens (found in bone) and keratin (found in claws and beaks), and are insoluble in all solvents. Others, such as albumins or globulins of plasma, are very soluble in water. Still others, which form part of membranes of cells, are partly hydrophilic ( water-loving , hence water-soluble) and partly lipophilic ( lipid-loving , hence fat-soluble). 

After secretion from the cell, certain lysyl residues of tropoelastin are oxidatively deaminated to aldehydes by lysyl oxidase, the same enzyme involved in this process in collagen. However, the major cross-links formed in elastin are the desmosines, which result from the condensation of three of these lysine-derived aldehydes with an unmodified lysine to form a tetrafunctional cross-hnk unique to elastin. Once cross-linked in its mature, extracellular form, elastin is highly insoluble and extremely stable and has a very low turnover rate. Elastin exhibits a variety of random coil conformations that permit the protein to stretch and subsequently recoil during the performance of its physiologic functions. 

Random collagen fibres provide an insoluble gel-like primary network and polyanionic hyaluronic acid a secondary network, which confers the viscoelastic property and stabilizes the collagen network (Balzas and Delinger, 1984). 

Scleroproteins, insoluble in most solvents. Localized in connective tissue, bone, hair, and skin. The two principal classes are the collagens and keratins Nucleoproteins, nucleic acid... 

All the tannins readily react with proteins, forming insoluble, stable compounds when they react with collagen, the main constituent of animal skin, they form leather, a material that is resistant to hydrolysis, oxidation, and biological attack and therefore stable to weathering and resistant to decomposition. Since tannins from different plant sources have different chemical compositions, each tannin used for tanning skin produces a leather having slightly different properties and color. Tannins that have... 

On a larger scale, we have ligaments and cartilage, structures that hold joints together and tie muscle to bone. These too are composed of proteins tough, water-insoluble proteins. Principal among them are the collagens. 

Volpin D and Veis A (1973) Cyanogen bromide peptides from insoluble skin and dentin bovine collagens. Biochemistry 12, 1452-1464. 

LaBella F, Waykole P and Queen G (1968) Formation of insoluble gels and dityrosine by the action of peroxidase on soluble collagens. Biochem Biophys Res Comm 30, 333-338. 

Collagens are quantitatively the most abundant of animal proteins, representing 25% of the total. They form insoluble tensile fibers that occur as structural elements of the extracellular matrix and connective tissue throughout the body. Their name (which literally means glue-producers ) is derived from the gelatins that appear as a decomposition product when collagen is boiled. 

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