Fig. 3.

Space-filling view of the two channels on opposite surfaces of the asymmetric dimer. The channels are at the dimer interface, with chain A mostly to the upper left in the view of channel 1 and to the lower right in the view of channel 2. The two views are related by a 180° rotation about the noncrystallographic 2-fold axis. Negatively charged residues that line the channels are colored red, positively charged residues are colored blue, and hydrophobic residues are colored yellow. The suffix a or b on the amino acid designations indicates whether the residue is from chain A or B. Arrows point to the parts of channel 1 that house AcCoA and polyamine. Channel 2 is occluded by residues 27–29 of chain B, which prevents polyamine but not CoA from binding.