  Amino acids are building-blocks of proteins, basic constituents of all
organisms and essential to life on Earth. They are present in carbonaceous
chondrite meteorites and comets, but their origin is still unknown. Formation
of amino acids in the interstellar medium is posible via specific gas-phase
reactions in dark clouds, however sensitive radiosearches at millimeter
wavelengths have not revealed their existence yet. The mid-IR vibrational
spectra of amino acids provides an alternative path for their identification.
We present Spitzer spectroscopic observations in the star-forming region IC 348
of the Perseus Molecular Cloud showing the detection of mid-IR emission lines
consistent with the most intense laboratory bands of the three aromatic amino
acids, tyrosine, phenylalanine and tryptophan and the aliphatic amino acids
isoleucine and glycine. Estimates of column densities give values 10-100 times
higher for isoleucine and glycine than for the aromatic amino acids as in some
meteorites. The strongest bands of each amino acid are also found in the
combined spectrum of >30 interstellar locations in diverse star-forming regions
supporting the suggestion that amino acids are widely spread in interstellar
space. Future mid-IR searches for proteinogenic amino acids in protostars,
protoplanetary disks and in the interstellar medium will be key to establish an
exogenous origin of meteoritic amino acids and to understand how the prebiotic
conditions for life were set in the early Earth.
