Rhodopsin is a G-protein-coupled receptor that is available from natural sources. The extraction of frog rod cell membranes with detergent resulted in the formation of two-dimensional crystals. The crystal suspension was put on carbon coated grids which were flash frozen in liquid ethane. Images of tilted specimens were recorded at liquid nitrogen temperature with a cold stage on an electron microscope. From several hundred images of tilted specimens, 60 crystalline areas were selected. Amplitudes and phases were extracted by computer image processing from the electron micrographs. The three-dimensional map had an effective resolution of about 7.5Å. A solid model of the frog rhodopsin map was constructed from 33 contour sections 2Å apart. The cytoplasmic side is at the top and the extracellular side is at the bottom.

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