Asparagine degradation

NG (AC-5) 5-cholesten-3)3-01 (sole carbon source - effect of nutrients) (with asparagine - no reaction) (without asparagine - degradation) A-19... 

FIGURE 3 Deamidation of asparagine by succinimide formation. L-aspartic acid and L-isoaspartic acid residues are the products of L-asparagine degradation via a succinimide intermediate. Aspartic acid residues can also form the succinimide intermediate by a similar mechanism with a loss of water. Figure based on that of Clarice et al. ... 

Fig. 6. Pathways of asparagine degradation in leaves of Pisum sativum. (1) Asparagine-oxoacid aminotransferase, (2) reduction, (3) asparaginase, (4) co-amidase, (S) aspartate-oxoglutarate aminotransferase, (6) malate dehydrogenase. (From Sieciechowicz et al., 1988a.) GLYOX, Glyox-ylate HOBA, 4-hydroxy 2-oxobutyrate HSE, homoserine PYR, pyruvate OSA, 2-oxosuccinamic acid HSA, hydroxysucdnamic add OAA, oxaloacetate MAL, malate OG, oxyglutarate.

L-Asparagine, systematic name, formula, and molecular weight, 2 558t Asparagus, citric acid in, 6 632t Aspartame, 2 605-606 12 42- 24 226-231 degradation of, 24 227—229 FDA approval of, 24 227 maleic anhydride in the manufacture of, 15 513... 

Asparagine residues (and glutamine residues, see below) are sites of particular instability in peptides. As will be exemplified below, rates of degradation at asparagine residues are markedly faster (tenfold and even much more) than at aspartic acid residues. As reported, the tm values for the internal asparagine in a large number of pentapeptides ranged from 6 to 507 d under... 

The simplest degradation displayed by asparagine and glutamine is direct hydrolytic deamidation of the side-chain carboxamido group (Fig. 6.29, Pathway d). Such a reaction, however, is seen only at low pH values, and its biological significance appears negligible. Its product is the Asp peptide (6.62) whose further reactions have been presented in Fig. 6.27. 

The most important degradation mechanism of asparagine and glutamine residues is formation of an intermediate succinimidyl peptide (6.63) without direct backbone cleavage (Fig. 6.29, Pathway e). The reaction, which occurs only in neutral and alkaline media, begins with a nucleophilic attack of the C-neighboring N-atom at the carbonyl C-atom of the Asn side chain (slow step). The succinimide ring epimerizes easily and opens by hydrolysis (fast step), as shown in Fig. 6.27, to yield the iso-aspartyl peptide (6.64) and the aspartyl peptide (6.65) in a ratio of 3 1. 

To summarize, the most frequently observed products of degradation at asparagine sites are ... 

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

To illustrate some of the above points, the degradation of a few selected bioactive peptides containing asparagine and glutamine residues will be described. 

Figure 10.10 Stability studies analysis by LC-MS. Long-term stability studies (3 months, 30°C) are evaluated by LC-MS analysis of a C-terminal peptide fragment. Various degradation mechanisms are visualized, removal of C-terminal residues due to proteolytic activities, isomerization and deamidation of specific asparagine residues. Future development efforts will allow the use of this methodology to assess progress toward a stable formulation.

Swainsonine (1) is of great biochemical interest since it is a potent and specific inhibitor of both lysosomal a-mannosidase and mannosidase II, which are involved in the cellular degradation of polysaccharides and in the processing of asparagine-linked glycoproteins, respectively [1]. 

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