Other Crosslinkages

The chain formed by polymerization of amino acid molecules provides the primary structure of a protein. Together with any covalent crosslinkages and other modifications, this may also be called the... 

Note that MIB-1 antibody fails to react with Ki-67 antigen in the tissue fixed with formaldehyde or Kryofix in the absence of heat pretreatment. Because Kryofix is a nonprotein, crosslinking fixative, breakdown of protein crosslinkages is not responsible for the availability of Ki-67 antigen in this case. On the other hand, MIB-1 antibody readily reacts with Ki-67 antigen in tissue fixed with cither of these two fixatives with heat pretreatment. It is apparent that in this case the effect of heat treatment is due to factors other than breakdown of protein crosslinkages. 

Despite these complications periodate oxidation is a convenient approach to reactive polysaccharide derivatives. The procedure is rather simple and in contrast with most other activation methods the activated polymer can be isolated in dry form without irreversible crosslinkage taking place. 

About 25 different human genes encode the keratins of skin and other soft tissues. Others specify the keratins of hair and nails.Both of these hard tissues as well as claws, hoofs, beaks, horns, scales, quills, and feathers are largely keratin. However, there are additional constituents. During the final stages of keratinocyte differentiation a 15-nm-thick crosslinked sheath of protein, the cornified cell envelope (CE), forms beneath the plasma membrane. Crosslinkages between keratin and other proteins are formed by the action of transglutaminases. " ... 

Figure 1.8 Vulcanization of natural rubber with sulfur, (a) Linear polyisoprene (natural rubber), (b) An idealized stmcture produced by vulcanization with sulfur. The number (x) of sulfur atoms in sulfide crosslinkages is 1 or 2 in efficient vulcanization systems but may be as high as 8 under conditions where cyclic and other structures are also formed in the reaction, (c) The effect of crosslinldng is to introduce points of linkage or anchor points between chain molecules, restricting their slippage.

Problem 3.20 The structure of a three-dimensional random network may be described quantitatively by two quantities the density of crosslinking designated by the fraction e of the total structural units engaged in crosslinkages and the fraction 6f of the total units which occurs as terminal units or free chain ends (i.e., which are connected to the structure by only one bond). Alternative quantities, such as the number (mole) N of primary molecules and the number (mole) v of crosslinked units, in addition to M and Me, defined above, are also used to characterize a random network stmeture. Relate N and v to these other quantities. 

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