Proteolytic susceptibilities

Furthermore, this combination caused a multifold increase in proteolytic susceptibility of oxidatively damaged BSA [7]. These findings are really confusing because superoxide and hydroxyl radicals react with each other with a diffusion-controlled rate to form inactive hydroxyl anion and dioxygen ... 

Rinas, U., Tsai, L.B., Lyons, D., Fox, G.M., Stearns, G., Fieschko, J., Fenton, D., and Bailey, J.E. (1992). Cysteine to serine substitutions in basic fibroblast growth factor effect on inclusion body formation and proteolytic susceptibility during in vitro refolding. Bio/Technology 10,435 440. 

Structural modifications and formulation are two additional approaches proposed for overcoming the enzymatic barrier (and references therein). Using recombinant or synthetic techniques, selective modifications to the protein or peptide sequence can be introduced effectively reducing proteolytic susceptibility, but these changes must not have significant impact on the pharmacological properties of the molecule (e.g., reduced potency or altered selectivity). Moreover, modifications to address a specific enzymatic action will not eliminate vulnerability to others. The formulation approach essentially involves encapsulation systems to protect the protein or peptide from reactions with enzymes, and selected examples include emulsions, liposomes, or enteric-coated capsules (and references therein). 

One of the requirements for the degradation of oxidized proteins by the 20S proteasome is its activation, very often occurring due to proteasome isolation or by low levels of SDS. This feature of increased proteolytic susceptibility due to moderate oxidation and a loss of proteolytic susceptibility due to excessive oxidation seems to be independent of the protein substrate and the oxidant used. 

Figure 37.6 Effect of flavin cofactor binding on the stability of the human electron-transfer flavoprotein (ETF) mutant variant Aspl28Asn. (A) Activity of the protein is affected by incubation at 39 °C (open circles) however, in the presence of 2.5-fold excess FAD the activity is preserved (black circles). (B) The stability of ETF Aspl28Asn to urea-induced chemical denaturation is higher when the flavin is bound to the protein (black circles) than in flavin-depleted ETF (open circles). (C) The presence of flavin cofactor affects the proteolytic susceptibility of ETF Aspl28Asn. Upon incubation with trypsin protease ETF Aspl28Asn is rapidly degraded (top panel), whereas in the presence of excess flavin, the protein is more resistance to proteolysis.

Copper salts such as CuS04 are potent catalysts of the oxidative modification of LDL in vitro (Esterbauer et al., 1990), although more than 95% of the copper in human serum is bound to caeruloplasmin. Cp is an acute-phase protein and a potent inhibitor of lipid peroxidation, but is susceptible to both proteolytic and oxidative attack with the consequent release of catalytic copper ions capable of inducing lipid peroxidation (Winyard and... 

The coupling of hirudin to polyethylene glycol (PEG) increases its half-life. PEG-hirudin is also less susceptible to proteolytic degradation (60). 

Proteins differ greatly in their intrinsic susceptibility to proteolytic attack. Resistance to proteolysis seems to be dependent upon higher levels of protein structure (i.e. secondary and tertiary structure), as tight packing often shields susceptible peptide bonds from attack. Denaturation thus renders proteins very susceptible to proteolytic degradation. 

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