Glutamine residues, reactivity

As in the case of degradation at aspartic acid residues, the major structural factors that influence the reactivity of asparagine and glutamine residues... 

In addition to the amino acids described above, several other amino acid residues are also reactive toward compounds containing heavy atoms. These are the side chains of arginine, asparagine, glutamine, lysine, tryptophan, and tyrosine. Those that are not reactive are alanine, glycine, isoleucine. 

Simply incubating a protein solution with the enzyme at a certain temperature can carry out the crosslinking of proteins by transglutaminase. The outcome, however, depends on several factors, including the ratio of enzyme to substrate (E/S), the reaction conditions, and the reactivity of protein substrates. As it has already been mentioned, some proteins can hardly be crosslinked by transglutaminase, although they contain both glutamine and lysine residues. Therefore, the reactivity of the protein substrate is the most important factor that... 

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