Models for depolymerizing enzymes: criteria for discrimination of models.

Several models for the action of alpha amylase have been proposed to account for the nonrandom distribution of oligosaccharides in the amylase digests of polysaccharides. The preferred-attack model attempts to account for the nonrandom distribution by assuming that the probability for bond cleavage depends upon the position of the bond in the chain. The repetitive, or multiple-attack, model suggests that the nonrandom distribution of oligosaccharides arises because an amylase can form a cage-like complex with a substrate and attack it several times during a single encounter. The multiple-enzyme or dual-site model suggests that the nonrandom yield of oligosaccharides arises from the combined action of exo- and endo-enzymes. The effects of pH, inhibitors, and substrate chain-length on enzyme action have been studied in several laboratories to determine which of the three action-patterns best describes the action of alpha amylase. The influence of these variables on product distributions or enzyme action-patterns are mathematically modeled in the Appendix. The experimental data on porcine-pancreatic alpha amylase are discussed in the light of the derivations.