Disulfide bonds, reduction inhibitory activity

The in vitro digestibility of heat-treated soybean protein by trypsin was increased by the breakage of disulfide bonds (269). This was caused primarily by increased digestibility of the trypsin inhibitors which are about 6% of the total protein. Even though the trypsin inhibitory activity had been destroyed by heat, the trypsin inhibitors were not readily hydrolyzed by trypsin until the disulfide bonds were broken by reduction or oxidation. m ... 

Considerable homology exists within the binding sites of several of the inhibitors as shown in Table VII. It has been suggested that trypsin inhibitors require a peptide sequence of Lys-X or Arg-X located within a loop of the protein closed by a disulfide bond (95,96). Reduction of disulfide bonds are known to be quite effective in destroying the inhibitory activity (77). For example, activity of the three isoinhibitors from Brazilian pink beans against both trypsin and chymotrypsin was lost when a specific disulfide bond, of the 18-21 disulfide bonds present, was reduced (77) SER appears to be a requirement of the binding site also for lysine-type inhibitors (Table VII). 

Choleragen (cholera toxin) exerts its effects on animal cells by activating adenylate cyclase, thereby increasing intracellular cAMP content (1). The Ai protein of choleragen, released from the holotoxin by reduction of a single disulfide bond linking the Ai and A2 proteins, catalyzes the mono-ADP-ribosylation of Gso, a regulatory component of the adenylate cyclase system that is responsible for the GTP-dependent activation of the cyclase catalytic unit. ADP-ribosylation of Gsa apparently increases its sensitivity to GTP and its dissociation from the inhibitory Gpy complex (1). 

Plunkett, G., and Ryan, C. A. (1980). Reduction and carboxamido-methyl ati on of the single disulfide bond of proteinase inhibitor I from potato tubers. Effects on stability, immunological properties, and inhibitory activities. J. Biol. Chem. 255, 2752-2755. 

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