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Electron microscopy of beef heart F1-ATPase crystals.

1983; Elsevier BV; Volume: 258; Issue: 5 Linguagem: Inglês

10.1016/s0021-9258(18)32852-7

1083-351X

Christopher W. Akey, Vitaly L. Spitsberg, Stuart J. Edelstein,

RNA and protein synthesis mechanisms

The structure of thin crystalline plates of beef heart F1-ATPase has been investigated by a combination of electron microscopy and computer-based image processing.Both negatively stained thin crystals and thin sections of embedded crystals were used in the analysis.Some inherent twinning was observed in the thin crystals and two distinct orthorhombic crystal forms present in the microcrystal population were characterized.The form I crystals are space group PZ1Z12 with unit cell parameters of a = 164 A, b = 324 A, and c = 118 di.The form I crystals have 1 molecule of beef heart coupling factor-ATPase/asymmetric unit and averaged reconstructions of projections of the (001) and (100) planes allowed the deduction of the packing of single F1-ATPase complexes in the crystals.The form I1 crystals have unit cell parameters of a = 156 A, c = 162 A, fi = 90" and are either space group P21212 or P2221.Furthermore, based on the results presented in this report, it is clear that the monoclinic crystalline inclusions which have been observed in human mitochondria are not directly related to the form I or form I1 crystals of the F1-ATPase.The P1-Fo complex from mitochondria appears to be a tripartite structure (l), composed of an Fo-sector intrinsic to the membrane, a central stalk portion, and an Fi-sector extrinsic to the membrane (2).The entire complex is composed of at least 9 polypeptide chains (3) and catalyzes the vectorial translocation of €I* coupled with the synthesis of ATP in a manner consistent with the chemiosmotic theory (4).The molecular weight of the F1-sector has been determined by a variety of techniques with values ranging from 320,000 to 385,000 (5).The molecular weights of the five subunits as determined by SDS'-gel electrophoresis are: a, 60,000; p, 56,000; y, 34,000; 6, 13,000; and E, 8,000 (6).Various subunit stoichiometries have been proposed for F,-ATPases isolated from bacteria (PS3, Escherichia coli, and Streptococcus fueculis), yeast, spinach chloroplasts, and mammalian mitochondria (rat liver and beef heart).No general consensus has yet emerged for the subunit structure of the F1-ATPase, as both a&y& (7,8) and cy3pBy& models (9-14) have been proposed.Divergence of the st.oichiometry of the major subunits of the