ELECTRON-MICROSCOPY OF BEEF-HEART MITOCHO NDRIAL ATP SYNTHASE

Two-dimensional crystals of the mitochondrial ATP synthase up to 0.4 m um in size were obtained from the detergent-lipid-protein micelles by detergent dialysis. A projected map of the negatively stained crystal was calculated from electron microscopical images by the Fourier-filte ring procedure at ca. 2.8 nm resolution. The unit cell (with not more than two ATP synthase molecules) has the following parameters: a 13.0 nm, b 25.6 nm and gamma 86-degrees. In line with this conclusion, two alternative models for the crystal structural organization are plausib le, viz., with one or two protein molecules per unit cell. The first m odel suggests an asymmetric incorporation of ATP synthase molecules in to the lipid bilayer: extramembranous portions F1 are located on one s ide of the crystal membrane plane. According to the second model, the incorporation occurs on each side of the lipid bilayer, the unit cell containing the two oppositely oriented protein molecules. Based on the absence of another type of the projected crystal images (a rear view of the membrane), unique to the first model, preference is given to th e second model.