The 8-amino-7-oxopelargonate synthase (AOPS) cloned from Bacillus sphaericus, overproduced in Escherichia coli, has been crystallized in the pyridoxal 5'-phosphate (PLP)-bound form at pH 7.5, using polyethylene glycol as the precipitant. One crystal form corresponds to a tetragonal space group, with unit-cell dimensions a = b = 66, c = 181 A. These crystals do not diffract beyond 5 A, with conventional X-ray sources and cannot be used in the structure elucidation. A second crystal form is obtained when crystallization conditions are varied slightly by the addition of 0.2 M ammonium sulfate. The space group is P2(1)2(1)2(1), with unit-cell dimensions a = 68.9, b = 85.5, c = 125.9 A, indicating the presence of two molecules in the asymmetric unit (V(m) = 2.26 A(3) Da(-1); 46% water). These crystals diffract X-rays up to 3.2 A using in-house facilities and a preliminary data set has been collected. A second data set using the synchrotron radiation source W32 at LURE (Paris) has shown the crystals to diffract to at least 3 A, resolution, with good statistics. The structure determination of AOPS will provide a structural framework for the other alpha-amino ketone synthases for which no three-dimensional structure is yet available.