The NAD(P)H dehydrogenase (NDH) complex in chloroplasts mediates photosystem I cyclic and chlororespiratory electron transport. Eleven chloroplast genes and three nuclear genes have been identified as encoding Ndh subunits, but the entire subunit composition is still unknown. An Arabidopsis (Arabidopsis thaliana) chlororespiratory reduction (crr3) mutant was isolated based on its lack of transient increase in chlorophyll fluorescence after actinic light illumination; this was due to a specific defect in accumulation of the NDH complex. The CRR3 gene (At2g01590) encodes a novel protein containing a putative plastid-targeting signal and a transmembrane domain. Consistent with the gene structure, CRR3 localized to the membrane fraction of chloroplasts. In addition to the essential function of CRR3 in stabilizing the NDH complex, the NDH complex is also required for the accumulation of CRR3. These results suggest that CRR3 interacts with the NDH complex in the thylakoid membrane. In contrast to other subunits in the chloroplast NDH complex, CRR3 is not conserved in cyanobacteria from which the chloroplast NDH complex is believed to have originated. We propose that CRR3 is a subunit of the NDH complex, which is specific to the chloroplast.

Calditocaldarchaeol (neutral tetraether lipid) from Sulfolobus acidocaldarius (acidothermophilic archaea) and intact total lipid from the thermoacidophilic archaea Sulfolobus sp. was examined by electrospray ionization time-of-flight mass spectrometry in the negative-ion mode using high resolution. When the sample was injected as a solution in a 3:1 mixture of methanol (MeOH) and chloroform (CHCl(3)) using an infusion system, the total ether lipid afforded molecular-related ions as [M - H](-) for acidic polar lipids containing a phosphoric or sulfuric group, and as [M + Cl](-) ion for neutral glycolipids. The attachment of chloride was confirmed by the observation of [M + Br](-) ion, instead of [M + Cl](-) ion, when a 3:1 mixture of MeOH and CHBr(3) was used in place of MeOH-CHCl(3) as the solvent. The composition of tetraether neutral glycolipids that are different from each other only in the number of five-membered rings in the isoprenoid chain was determined on the basis of the isotope-resolved mass spectrum of [M + Cl](-) ions. As for acidic tetraether lipids, molecular-related ions [M - H](-)) were not observed when the 3:1 MeOH-CHBr(3) mixture was used as the solvent. These results together afforded a facile method of distinguishing neutral from acidic tetraether lipids in intact total lipids of acidothermophilic archaea. This method was applied to determine the difference of the number of five-membered rings in isoprenyl chains of neutral tetraether glycolipids yielded by the Sulfolobus sp. grown at different temperatures. Discrimination of neutral tetraether glycolipids from acidic tetraether lipids in the total lipids obtained from Thermoplasma sp. was also achieved by this method.

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