Modulation of protease specificity by a change in the enzyme microenvironment. Selectivity modification on a model substrate, purified soluble proteins and gluten.

Subtilisin BPN' activity on a synthetic substrate is found to decrease with the concentration of soluble additives such as sugars and polyols, the catalytic efficiency of the enzyme being related to the water activity in the reaction medium. Limited hydrolysis of B chain of insulin is followed and the cleavage priority determined. When carried out in glycerol-containing medium, both enzyme catalytic behaviour and specificity are perturbed; a different cleavage order and a selectivity restriction are observed. The experiments were generalised to purified proteins and to an insoluble protein complex. The hydrolysis kinetics of purified gliadins by pepsin and of gluten by a Bacillus neutral protease are modulated in presence of water activity depressors. Glycerol is able to increase both pepsin efficiency and gluten protein solubility. The hydrolysis order is affected by water-structuring molecules in the enzyme microenvironment and new peptides appear whatever the size and initial solubility of the substrate.