Monte Carlo simulation of multiple attack mechanism of alpha-amylase.

Porcine pancreatic alpha-amylase (EC 3.2.1.1) produces short maltooligosaccharides from a single enzyme-substrate complex without dissociation by multiple or repetitive attack. Multiple attack is caused by relative sliding of the enzyme along the product chain of the enzyme-product complex without dissociation to form another productive complex. The Monte Carlo method was applied to the multiple attack mechanism to predict product distribution from amylose and amylopectin molecules of arbitrary sizes. The position of the initial attack to make the enzyme-substrate complex and branched reaction paths from the enzyme-product complex were selected by random numbers and probabilities. A simulated product distribution from 100,000 samples of amylose of chain length greater than 80 agreed completely with experimental data at the early stage of hydrolysis of amylose of mean chain length 90. On the other hand, the simulated product distribution from amylopectin agreed with experimental data of potato amylopectin when the effective chain length of the A chain was 9. Since the mean chain length of the A chain of potato amylopectin is 15, it is possible that amylopectin is partially compact in solution, so that the enzyme can recognize and act only on the outer side of the A chain at the early stage of digestion.