Catalytic activity of aspartate aminotransferase in the crystal. Equilibrium and kinetic analysis.

Natural substrates and analogs rapidly diffuse through crystals of pig heart mitochondrial aspartate aminotransferase and react at the active sites causing spectral changes that can be measured by single-crystal microspectrophotometry. Dissociation constants for natural substrates and rate constants of transamination for slowly reacting substrates have been determined. A comparison between the data obtained in the crystal and in solution shows that the crystalline enzyme is catalytically competent and that events occurring in the crystal essentially parallel those occurring in solution, even though minor differences have been detected.