Polypeptides: crosslinking: functionalization

Likewise, in the preparation of many ion-exchange resins, suitable functional groups are introduced by secondary reactions of macromolecular substances (that are generally crosslinked see Sect. 5.2). In this context the utilization of crosslinked polystyrene resins or poly(acrylamide) gel in the solid-phase synthesis of polypeptides (Merrifield technique) or even oligonucleotides should be mentioned. After complete preparation of the desired products they are cleaved from the crosslinked substrate and can be isolated. 

In each of these formulas additional free OH groups are available on the silicon so that it is possible to crosslink more than two polysaccharide chains. Silicon may function as a biological crosslinking agent in connective tissue. Silaffins, small polypeptides containing polyamine side chains of modified lysine residues, apparently initiate silica formation from silicic acid in diatoms.0... 

The sequence of amino acids in the chain of a protein is of critical importance in the biological functioning of the protein, and its determination is very difficult. The chains may be relatively straight, or they may be coiled or helical, In the case of certain types of polypeptides, such as the keratins, they are crosslinked by the disulfide bonds of cystine. Linear polypeptides can be regarded as proteins. See also Amino Acids and Proteins. 

Several conclusions can be reached from this study. First, multiple GroEL apical domains indeed bind to substrate polypeptides, both in vivo and in vitro, and this ability appears to be crucial to the cellular function of GroEL. This is supported by the additional demonstration that non-native Rubisco bound to a GroEL containing an apical cysteine residue made disulfide crosslinks to multiple GroEL subunits. Second, different substrates have different requirements for the apical domains, stringent substrates such as MDH and Rubisco being the most... 

---