Structure of oligomeric and polymeric forms of ox liver glutamate dehydrogenase examined by electron miroscopy

Abstract

Commercial preparations of glutamate dehydrogenase have been examined in the electron microscope by the negative staining technique. When stained with sodium phosphotungstate all the preparations consisted almost entirely of trimeric structures identical in appearance with structures described by other workers. These particles were also present in preparations negatively stained with ammonium molybdate; but suspensions of crystals of the enzyme examined in this stain also contained polymers made up of the particles. Six morphologically distinguishable polymers have been recognised; four of these are tubular and contain helically wound filaments. The crystals seen in the lightmicroscope are formed from bundles of one or other of the tubular polymeric forms. The differences between the tubular forms of the polymers are due to differences in the number of filaments of which they are composed and variability in the packing of the individual particles which make up the filaments.