3-DIMENSIONAL STRUCTURE OF MITOCHONDRIAL ASPARTATE-AMINOTRANSFERASE AT 4.5-A RESOLUTION

An X-ray crystallographic study at 4.5 Å resolution has been carried out with triclinic crystals of chicken mitochondrial aspartate aminotransferase. In the electron density map, the enzyme is clearly visible as an isologous α2-dimer (105 Å × 60 Å × 50 Å) in which the subunits are associated about a molecular 2-fold axis. Each subunit of dimensions 70 Å × 50 Å × 40 Å contains at least seven helices, one of which is about 50 Å long. Difference maps have revealed the positions of the pyridoxyl and the phosphate moieties of the coenzyme as well as the general substrate binding area. The active sites are on opposite sides of the dimer, about 30 Å apart and close to the intersubunit boundary, so that probably both subunits contribute to each active site. An isolated chain segment, passing in front of the active site and ending in contact with the neighbouring subunit is interpreted as one of the chain termini. © 1979.