Monte Carlo simulation of 4-alpha-glucanotransferase reaction.

4-alpha-Glucanotransferase (GTase, D-enzyme) catalyzes disproportionation between two short polymers of maltooligosaccharides linked by alpha-1,4-glucoside bonds. Using action modes of the potato GTase for the donor and acceptor substrates, the Monte Carlo method was applied to simulate the GTase reaction. The simulation starts from a single enzyme molecule and a finite number (10(5)) of substrate molecules. All selection processes were performed using random numbers produced by computer. The initial substrates were from trimer to 10-mer. In every case, the final stage was the steady-state distribution of polymers. The steady-state distribution by the potato GTase reaction was different from those by the hypothetical random disproportionation reaction. The simulated data from the reaction of potato GTase and trimer almost quantitatively agreed with experimental data. The mechanism of the GTase reaction was accumulation of probabilistic processes and was well simulated by the Monte Carlo method. GTase randomizes the overall distribution of chain length of the substrate. Therefore the GTase reaction is an entropy-driven process.