  Baryon distribution amplitudes (DAs) are crucial for the theory of hard
exclusive reactions. We present a calculation of the first few moments of the
leading-twist nucleon DA within lattice QCD. In addition we deal with the
normalization of the next-to-leading (twist-four) DAs. The matrix elements
determining the latter quantities are also responsible for proton decay in
Grand Unified Theories. Our lattice evaluation makes use of gauge field
configurations generated with two flavors of clover fermions. The relevant
operators are renormalized nonperturbatively with the final results given in
the MSbar scheme. We find that the deviation of the leading-twist nucleon DA
from its asymptotic form is less pronounced than sometimes claimed in the
literature.
