  Two isoforms of beta amyloid peptides, Ab40 and Ab42, differ from each other
only in the last two amino acids, IA, at the end of Ab42. They, however, differ
significantly in their ability in inducing Alzheimer's disease (AD). The rate
curves of fibril growth of Ab40 and Ab42 and the effects of molecular crowding
have been measured in in vitro experiments. These experimental curves, on the
other hand, have been fitted in terms of rate constants for elementary reaction
steps using rate equation approaches. Several sets of such rate parameters have
been reported in the literature. Employing a recently developed stochastic
kinetic method, implemented in a browser-based simulator, popsim, we study to
reveal the differences in the kinetic behaviors implied by these sets of rate
parameters. In particular, the stochastic method is used to distinguish the
kinetic behaviors between Ab40 and Ab42 isoforms. As a result, we make general
comments on the usefulness of these sets of rate parameters.
