Hydrolysis isopeptide bond

Hydrolysis of the Isopeptide Bond. The bio availability of methionine covalently linked to casein has been studied by the response (protein efficiency ratio) of rats that have been fed the modified protein (23,63). The covalently bound methionine appears to be as available as the free amino acid. This finding indicates that there is an efficient enzymatic... 

Ubiquitin is highly conserved in eukaryotes yeast and human ubiquitin differ at only 3 of 76 residues. The carboxyl-terminal glycine residue of ubiquitin (Ub) becomes covalently attached to the e-amino groups of several lysine residues on a protein destined to be degraded. The energy for the formation of these isopeptide bonds (iso because e- rather than a-amino groups are targeted) comes from ATP hydrolysis. 

The major problem in all work carried out on isopeptides was related to the fact that the isopeptide bond is chemically an amide bond and as a consequence of this is susceptible to attack by acids or alkalis, thus destroying the isopeptide. The only possible methods were microbiological or enzymic, both of which obviate the problem of random hydrolysis. Methods of enzymic digestion had previously been knowi and adequately used however, such methods, although suitable for globular proteins, proved to... 

These isopeptide bonds are cleaved during acidic hydrolysis of protein and, therefore, do not contribute to the occurrence of unusual amino acids. A more intensive heat treatment of proteins in the presence of water leads to a more extensive degradation. 

---