  Amino acids are building blocks of proteins and therefore key ingredients for
the origin of life. The simplest amino acid, glycine, has long been searched
for in the interstellar medium but has not been unambiguously detected so far.
Since the search for glycine has turned out to be extremely difficult, we aimed
at detecting a chemically related species (possibly a direct precursor), amino
acetonitrile. With the IRAM 30m telescope we carried out a complete line survey
of the hot core regions Sgr B2(N) and (M) in the 3 mm range, plus partial
surveys at 2 and 1.3 mm. We analyzed our 30m line survey in the LTE
approximation and modeled the emission of all known molecules simultaneously.
We identified spectral features at the frequencies predicted for amino
acetonitrile lines having intensities compatible with a unique rotation
temperature. We also used the VLA to look for cold, extended emission from
amino acetonitrile. We detected amino acetonitrile in Sgr B2(N) in our 30m
telescope line survey and conducted confirmatory observations of selected lines
with the IRAM PdB and the ATCA interferometers. The emission arises from a
known hot core, the Large Molecule Heimat, and is compact with a source
diameter of 2 arcsec (0.08 pc). We derived a column density of 2.8e16 cm-2, a
temperature of 100 K, and a linewidth of 7 km s-1. Based on the simultaneously
observed continuum emission, we calculated a density of 1.7e8 cm-3, a mass of
2340 Msun, and an amino acetonitrile fractional abundance of 2.2e-9. The high
abundance and temperature may indicate that amino acetonitrile is formed by
grain surface chemistry. We did not detect any hot, compact amino acetonitrile
emission toward Sgr B2(M) or any cold, extended emission toward Sgr B2, with
column-density upper limits of 6e15 and 3e12-14 cm-2, respectively. (abridged)

Astrophysics