Fluorescence spectroscopic methods were used to study the interaction between aspartate aminotransferase and glutamate dehydrogenase isolated from pig brain. The conversion of the P-pyridoxal form of the aminotransferase to the P-pyridoxamine form of the enzyme is easily monitored by recording emission spectra upon excitation at 330 nm. Evidence for the interaction between the enzymes was obtained from fluroescence measurements conducted on aspartate aminotransferase label with a fluorescence probe (1-5-AEDANS) attached to one sH residue of the protein. The interaction of the aminotransferase (1μM) with glutamate dehydrogenase (2μM) brings about an enhancement as well as a blue shift in the band position of the fluorescence emitted by the dansyl chromophore. Polarization of fluorescence measurements conducted over a wide range of temperatures reveal that the rotational correlation time of aspartate aminotransferase (35 n.seconds) is increased to a value of 100 n.seconds upon addition of glutamate dehydrogenase.