Comparison of Simulated Images With Electron Images of Lactic Dehydrogenase

Abstract

Comparison of negative stain images of glutamate dehydrogenase (GDH) with shadow projections of opaque models has revealed that this approach can be misleading. We have suggested an x-ray simulation procedure in which the influence on the image of disruption of oligomer, finite metal-ion complex size, and depth of the stain layer are simulated under controlled conditions, and have deduced a model of GDH quaternary structure using this procedure.Here the accuracy of procedure suggested above is tested by comparing micrographs of rabbit muscle lactic dehydrogenase (LDH) with simulated images obtained with a model of dogfish LDH constructed in accord with x-ray diffraction data. The dogfish and rabbit muscle LDH's exhibit extensive sequence homology, are each composed of four subunits, and have nearly identical molecular weights. Dogfish LDH exhibits 222 symmetry and the shape of the oligomer approximates a parallelepiped.