Threonine peptides, cleavage selective

In the bicyclic peptide phalloidine where there are three eligible hydroxyl groups, one /3-hydroxyl in a threonine residue, and a y- and 5-hydroxyl group in the 7,5-dihydroxy-L-leucine residue, the controlled action of sulfuric acid leads to formation of the y-lactone only with selective cleavage of one peptide bond (Wieland and Schopf, 1959). 

The oxidation of trypsin and trypsinogen was carried out in aqueous 0.1 M acetate buffer solutions at room temperature. In this particular case and under these conditions no significant cleavage of peptide bonds next to tryptophan residues occurred. Careful analysis of hydrolyzates of NBS-oxidized trypsinogen and trypsin confirmed the selectivity of the oxidative modification of the protein, as Table XXIV shows. There is no significant loss of tyrosine, histidine, serine, threonine, or cystine, although all of these amino acids will react with NBS but considerably less rapidly than tryptophan. 

Also suited for the specific enzymatic hydrolysis of peptide chains is the endoproteinase Glu-C from Staphylococcus aureus V8. It cleaves Glu-X bonds (ammonium carbonate buffer pH 7.8 or ammonium acetate buffer pH 4.0) as well as Glu-X plus Asp-X bonds (phosphate buffer pH 7.8). The most important chemical method for selective cleavage uses cyanogen bromide (BrCN) to attack Met-X-hnkages (Reaction 1.86). Hydrolysis of proteins with strong acids reveals a difference in the rates of hydrolysis of peptide bonds depending on the adjacent amino acid side chain. Bonds involving amino groups of serine and threonine are particularly susceptible to hydrolysis. This effect is due to... 

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