All 13 lipids, including two cardiolipins, one phosphatidylcholine, three phosphatidylethanolamines, four phosphatidylglycerols and three triglycerides, were identified in a crystalline bovine heart cytochrome c oxidase (CcO) preparation. The chain lengths and unsaturated bond positions of the fatty acid moieties determined by mass spectrometry suggest that each lipid head group identifies its specific binding site within CcOs. The X-ray structure demonstrates that the flexibility of the fatty acid tails facilitates their effective space-filling functions and that the four phospholipids stabilize the CcO dimer. Binding of dicyclohexylcarbodiimide to the O 2 transfer pathway of CcO causes two palmitate tails of phosphatidylglycerols to block the pathway, suggesting that the palmitates control the O 2 transfer process.The phosphatidylglycerol with vaccenate (cis-D 11 -octadecenoate) was found in CcOs of bovine and Paracoccus denitrificans, the ancestor of mitochondrion, indicating that the vaccenate is conserved in bovine CcO in spite of the abundance of oleate (cis-D 9 -octadecenoate). The X-ray structure indicates that the protein moiety selects cis-vaccenate near the O 2 transfer pathway against trans-vaccenate. These results suggest that vaccenate plays a critical role in the O 2 transfer mechanism.

NADH-ubiquinone oxidoreductase (Complex I) is located at the entrance of the mitochondrial electron transfer chain and transfers electrons from NADH to ubiquinone with 10 isoprene units (Q(10)) coupled with proton pumping. The composition of Complex I, the largest and most complex proton pump in the mitochondrial electron transfer system, especially the contents of Q(10) and phospholipids, has not been well established. An improved purification method including solubilization of mitochondrial membrane with deoxycholate followed by sucrose gradient centrifugation and anion-exchange column chromatography provided reproducibly a heme-free preparation containing 1 Q(10), 70 phosphorus atoms of phospholipids, 1 zinc ion, 1 FMN, 30 inorganic sulfur ions, and 30 iron atoms as the intrinsic constituents. The rotenone-sensitive enzymatic activity of the Complex I preparation was comparable to that of Complex I in the mitochondrial membrane. It has been proposed that Complex I has two Q(10) binding sites, one involved in the proton pump and the other functioning as a converter between one and two electron transfer pathways [Ohnishi, T., Johnson, J. J. E., Yano, T., LoBrutto, R., and Widger, R. W. (2005) FEBS Lett. 579, 500-506]. The existence of one molecule of Q(10) in the fully oxidized Complex I suggests that the affinity of Q(10) to one of the two Q(10) sites is greatly dependent on the oxidation state and/or the membrane potential and that the Q(10) in the present preparation functions as the converter of the electron transfer pathways which should be present in any oxidation state.

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Remineralization is the process by which hydroxyapatite (HAp) is restored in enamel subsurface lesions, and transversal microradiography (TMR) has been used to analyze remineralization in terms of the recovery of mineral content. In this study, we directly detected the distribution and orientation of longitudinal HAp crystallite at the remineralized zone in enamel subsurface lesions by using an X-ray microbeam (6-µm diameter) diffraction method. This method was demonstrated and involves the simultaneous detection of wide-angle X-ray diffraction (WAXRD) and small-angle X-ray scattering (SAXS). WAXRD reflects the amount of HAp crystallites, and SAXS reflects that of voids in crystallites. The polished surface of a bovine enamel block was divided into three zones of sound, demineralized, and remineralized zones. Thin sections of approximately 150 µm thickness were then cut perpendicular to the surface, and subjected to WAXRD and SAXS following TMR. The increase in the amount of HAp crystallites and the decrease in voids in the crystallites at the remineralized zone were detected by WAXRD and SAXS, respectively, which was consistent with the result of TMR. This study indicates that both the spatial distribution and orientation of the restored HAp crystals in the remineralization process at the subsurface lesion can be simultaneously analyzed by the X-ray diffraction methods.

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