  The peptides in biosystems are homochiral polymers of L-amino acids, but
razemisate slowly by an active isomerization kinetics. The chemical reactions
in biosystems are, however, reversible and what racemisates the peptides at the
water activity in the biosystems can ensure homochirality at a smaller
activity. Here we show by a thermodynamics analysis and by comprehensive
Molecular Dynamics simulations of models of peptides, that the isomerization
kinetics racemisates the peptides at a high water activity in agreement with
experimental observations of aging of peptides , but enhances homochirality at
a smaller water activity. The hydrophobic core of the peptide in an enzyme can
ensure homochirality at a low water activity, and thus the establishment of
homochirality at the origin of life and ageing of peptides and dead of
biosystems might be strongly connected.
