Optical properties and optical constituents of the Faroe Islands shelf and off-shelf waters,North East Atlantic

The study comprises a data set of CTD, optical properties—K ₀(PAR), c _p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005. Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C) and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K ₀(PAR), beam attenuation c _p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K ₀(PAR) was governed by Chl a, shown by a high (r ² = 0.64) Chl a–K ₀(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient K₀^* ( \textPAR ) K_{0}^{*} \left( {\text{PAR}} \right) of 0.056 (m² mg⁻¹ Chl a) and a Chl a specific beam attenuation ( c_\textp^* c_{\text{p}}^{*} ) of 0.27 (m² mg⁻¹ Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained in early spring, and Chl a concentrations were low ~0.5 mg Chl a m⁻³. Spring bloom Chl a are about 10 mg Chl a m⁻³ and estimations showed that shelf K ₀(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete data set is enclosed.     

In situ characterisation of photosynthetic electron transport in Rhodopseudomonas capsulata

1. The effects of varying the ambient oxidation/reduction potential on the redox changes of cytochromes c, cytochromes b and P605 induced by a laser flash in chromatophores from Rhodopseudomonas capsulata Ala Pho⁺ have been investigated.2. The appearance and attenuation of the changes with varying ambient redox potential show that, of the cytochromes present, cytochromes c with Em₇ = 340 mV and 0 mV, and cytochrome b, Em₇ = 60 mV were concerned with photosynthetic electron flow.3. The site of action of antimycin was shown to be between cytochrome b₆₀ and a component, as yet unidentified, called Z.4. The appearance or attenuation of laser-induced changes of cytochromes c₀ and b₆₀ on redox titration was dependent on pH, but no effect of pH on the cytochrome c₃₄₀ titration was observed.5. The dependence on ambient redox potential of the laser-induced bleaching at 605 nm enabled identification of the mid-point potentials of the primary electron donor (Em₇ = 440 mV) and acceptor (Em₇ = ?25 mV).6. The interrelationship of these electron carriers is discussed with respect to the pathway of cyclic electron flow.     

Scattering spectrum properties and their relationship to biogeochemical parameters: a case study in Taihu Lake

The scattering spectrum properties of highly turbid and eutrophic inland case 2 water from Taihu Lake were studied during three cruises from 2006 to 2007. The scattering [b _p(λ)] and backscattering [b _bp(λ)] coefficients and the backscattering probability (B) for Taihu Lake were found to show a clear spectral dependence, and this dependence was well simulated by a power-law function. This dependence, however, became weak when algae dominated the sample points. The mean values of the power-law index for b _p(λ), v, in Oct 2006, Mar 2007 and Nov 2007 were −0.6712, −0.8129 and −0.7600, respectively. To interpret the spectral characteristics and mechanisms of b _p(λ) and b _bp(λ), water samples were collected simultaneously for the biogeochemical characterization of suspended particles. The average values of the specific scattering coefficients for total suspended matter, inorganic suspended matter (ISPM) and organic suspended matter (OSPM) were 0.634 (550 nm), 1.057 (532 nm), and 0.396 g m⁻² (532 nm), respectively. The power-law index of b _bp(λ) (Y) was significantly related to ISPM/OSPM and b _bp(532 nm), but only weakly related to the particle size distribution index. The mean (spatial and wavelength) values of B in Oct 2006, Mar 2007, and Nov 2007 were 0.0108, 0.0138, and 0.0125, respectively. B decreases with increasing ISPM concentration because of the large contribution of ISPM to b _b(λ) and the strong restraint on b _bp(λ) caused by the multi-scattering effect under high-turbidity conditions.     

Functional Characterization and Partial Purification of the Ubiquinol-Cytochrome c Oxidoreductase from Higher Plant Mitochondria (Helianthus tuberosus)

The functional and thermodynamic characteristics of the ubiquinolcytochrome (Cyt) c oxidoreductase in a Cyt b/c₁-enriched fraction (defined S-1) isolated from Jerusalem artichoke mitochondria (JAM) (Helianthus tuberosus), have been analyzed. Fraction S-1, obtained through deoxycholate-KCl fractionation procedure, contained one Cyt of c type (formally c₁ with Em_7.0 of +240 millivolts), two b type Cyt with Em_7.0 values of +100 and −25 millivolts, ferredoxin-like centers presumably linked to succinic- and NADH-dehydrogenases, and a Rieske-type iron sulfur center (g_y = 1.89). The ubiquinol-dependent Cyt c reduction by fraction S-1 showed sensitivity to antimycin A, myxothiazol, and n-2-hepthyl-1-hydroxyquinoline N-oxide with I₅₀ of 12 nanomolar, 30 nanomolar, and 0.1 micromolar, respectively. Oxidation-induced extra b type reduction, a widespread phenomenon of bacterial and mitochondrial respiratory systems, has also been observed in both intact mitochondria and S-1 fraction. The data seem to blur previous experiments in which both spectral and functional differences between higher plant and mammalian mitochondria have been underlined.     

Electron paramagnetic resonance and Mössbauer spectroscopy of intact mitochondria from respiring <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Mitochondria from respiring cells were isolated under anaerobic conditions. Microscopic images were largely devoid of contaminants, and samples consumed O₂ in an NADH-dependent manner. Protein and metal concentrations of packed mitochondria were determined, as was the percentage of external void volume. Samples were similarly packed into electron paramagnetic resonance tubes, either in the as-isolated state or after exposure to various reagents. Analyses revealed two signals originating from species that could be removed by chelation, including rhombic Fe³⁺ (g = 4.3) and aqueous Mn²⁺ ions (g = 2.00 with Mn-based hyperfine). Three S = 5/2 signals from Fe³⁺ hemes were observed, probably arising from cytochrome c peroxidase and the a₃:Cu_b site of cytochrome c oxidase. Three Fe/S-based signals were observed, with averaged g values of 1.94, 1.90 and 2.01. These probably arise, respectively, from the [Fe₂S₂]⁺ cluster of succinate dehydrogenase, the [Fe₂S₂]⁺ cluster of the Rieske protein of cytochrome bc ₁, and the [Fe₃S₄]⁺ cluster of aconitase, homoaconitase or succinate dehydrogenase. Also observed was a low-intensity isotropic g = 2.00 signal arising from organic-based radicals, and a broad signal with g _ave = 2.02. Mössbauer spectra of intact mitochondria were dominated by signals from Fe₄S₄ clusters (60–85% of Fe). The major feature in as-isolated samples, and in samples treated with ethylenebis(oxyethylenenitrilo)tetraacetic acid, dithionite or O₂, was a quadrupole doublet with ΔE _Q = 1.15 mm/s and δ = 0.45 mm/s, assigned to [Fe₄S₄]²⁺ clusters. Substantial high-spin non-heme Fe²⁺ (up to 20%) and Fe³⁺ (up to 15%) species were observed. The distribution of Fe was qualitatively similar to that suggested by the mitochondrial proteome.     

Inhibition of Respiration in Prototheca zopfii by Light

Irradiation of cells of Prototheca zopfii with blue light inhibited the respiratory capacity of the cells. The inhibition of respiration was correlated with a photodestruction of cytochrome c(551), cytochrome b(559), and cytochrome a₃. Cytochrome c(549), cytochrome b(555), and cytochrome b(564) were unaffected by the irradiation treatment. The α-band of reduced cytochrome a was shifted from 599 to 603 nm by irradiation, an effect similar to that observed when methanol was added to nonirradiated cells. The presence of oxygen was required during irradiation for both photoinhibition of respiration and photodestruction of the cytochromes. Cytochrome a₃ was protected against photodestruction by cyanide. Photodestruction of these same cytochromes also occurred when washed mitochondria of P. zopfii were irradiated.     

A study of absorption characteristics of chromophoric dissolved organic matter and particles in Lake Taihu,China

Absorptions by non-phytoplankton particles and phytoplankton, and chromophoric dissolved organic matter (CDOM) were measured at 50 sites in large, shallow, Lake Taihu in winter and summer 2006 to study their seasonal and spatial variations, and their relative contributions to total absorption. The CDOM absorption was significantly higher in winter than in summer, due to degradation and release of fixed carbon in phytoplankton and submerged aquatic vegetation (SAV). The hyperbolic model was used to model the spectral absorption of CDOM, and the mean spectral slope of 6.38 nm⁻¹ was obtained. At most sites, the spectral absorption of non-phytoplankton particles was similar to that of the total particles, demonstrating that the absorption of the total particles is dominated by the absorption of non-phytoplankton particles. In summer, phytoplankton absorption increased markedly, due to frequent algal blooms especially in Meiliang Bay. In winter, the significant increase in non-phytoplankton particle absorption resulted from the increase of inorganic particulate matter caused by sediment resuspension. Strong linear relationships were found between a _d(440) and total suspended matter (TSM), organic suspended matter (OSM), and inorganic suspended matter (ISM). Strong linear relationships were also found between a _ph(440), a _ph(675) and chlorophyll a (Chl-a) concentration. The total relative contributions of non-phytoplankton particles over the range of photosynthetically active radiation (PAR) (400–700 nm) were 48.4 and 79.9% in summer and winter respectively. Non-phytoplankton particle absorption dominated the total absorption, especially in winter, in Lake Taihu, due to frequent sediment resuspension in the large shallow lake as a result of strong windy conditions. The results indicate that strong absorption by CDOM and non-phytoplankton particles at the blue wavelength has an impact on the spectral availability, and acts as a selection factor for the composition of the phytoplankton community, with cyanobacteria being the dominate species in Lake Taihu. Handling editor: L. Naselli-Flores     

The Cytochromes of Prototheca zopfii

The respiratory pigments of Prototheca zopfii include seven cytochromes: two c-type cytochromes, a soluble c(549) and a membrane bound c(551); three b-type cytochromes, b(555), b(559) and b(564); and cytochromes a and a₃. Cytochromes a and a₃ could be resolved spectrally in the α-band region by reducing the cells in the presence of methanol and cyanide. Methanol shifted the absorption maximum of cytochrome a from 598 to 603 nanometers and permitted dithionite (or substrate) to reduce the cyanide-cytochrome a₃ complex to give a well defined 595-nanometer absorption band. Methanol did not interfere with CO binding by cytochrome a₃, and CO did not alter the methanol effect on cytochrome a. Azide and cyanide, which partially inhibited exogenous respiration, stimulated endogenous respiration. Frozen steady states of the electron transport chain in the presence of cyanide and azide indicated that the stimulation by these inhibitors was due to an increased autooxidation of one of the b-type cytochromes, possibly b(564).     

Estuarine morphometry governs optically active substances, K d(PAR) and beam attenuation: assessments from a tropical ria and a temperate coastal plain estuary

Data on optical properties such as diffuse attenuation coefficient K _d(PAR), beam attenuation coefficient (c _p) and the optically active constituents (OACs) CDOM, Chl-a and suspended particulate matter were obtained in a Danish temperate coastal plain estuary (56°N) and a Vietnamese tropical ria (12°N) at high discharges. The major difference was the spatial distribution of the optical properties against distance, best described by significant power functions in the ria, compared to significant linear functions in the coastal plain. It was hypothesized that estuarine morphometry could explain this spatial distribution. Partition and multiple regression analyses showed that Chl-a governed K _d(PAR) and beam attenuation coefficient in both estuaries. Significant, high correlations were obtained by multiple regression analyses in the estimation of K _d(PAR) and beam attenuation coefficients in the two estuaries using OACs as input parameters. It is concluded that there are no large differences in OAC concentrations between the two estuaries. The spatial distributions of OACs and optical properties were significantly different and governed by the estuary morphometry, i.e. a power distribution in the tropical ria and a linear function in the temperate coastal plain estuary, and applicable to similar estuary types.     

Partitioning particulate scattering and absorption into contributions of phytoplankton and non-algal particles in winter in Lake Taihu (China)

Light scattering, backscattering, and absorption coefficients of particles were observed at 62 locations in Lake Taihu (China) in November 2008. A method using a priori knowledge and the measured data was proposed to partition particulate scattering and absorption into contributions of phytoplankton and non-algal particles. The results showed that phytoplankton weakly contributed to the particulate scattering and backscattering with the mean b _ph/b _p values usually below 10% and b _bph/b _bt values of 0.3–3.9% in the whole visible light spectrum, and an approximate relationship of b _bt ≈ b _bp ≈ b _bnap was regarded as reasonable in Lake Taihu. In contrast with scattering and backscattering, phytoplankton made more contributions to the particulate absorption with the mean a _ph/a _p values varying in a wide range of about 20–70%. Both the scattering and absorption spectra of non-algal particles can be modeled well by corresponding methods. A power function model was used to simulate the scattering spectra, which presented high predictive accuracies with MAPE values usually below 5% and RMSE values below 1.5 m⁻¹, while the spectral absorption model also performed well with mean S _nap being 0.0052 nm⁻¹ (standard deviation, SD = 0.0010 nm⁻¹). As to the phytoplankton absorption, a quadratic function model used was considered to have a good performance with corresponding parameters being supported at each wavelength in the spectral range of 400–700 nm. Additionally, two basic bio-optical parameters were determined, that is, b _nap^*(550) = 0.604 m² g⁻¹ and a _ph^*(675) = 0.0288 m² mg⁻¹. Overall, these results obtained in the present study supply us with new knowledge about optical properties of suspended particulates in an inland and highly turbid lake (Lake Taihu), which are beneficial to the development of analytical models of water color remote sensing.     

Thermodynamic and EPR characterization of mitochondrial succinate-cytochrome c reductase-phospholipid complexes

Succinate-cytochrome c reductase can be easily solubilized in a phospholipid mixture (1:1, lysolecithin:lecithin) in the absence of detergents. The resulting solution contains two b cytochromes with half-reduction potentials of 95 ± 10 mV (b₅₆₁), and 0 ± 10 mV (b₅₆₆) and cytochrome c₁ (E_{m 7.2} = +280±5 mV). The oxidation-reduction midpoint potentials obtained by optical potentiometric titrations are identical to those determined by the EPR titrations and are 40–60 mV higher than the corresponding midpoint potentials of these cytochromes in intact mitochondria. In contrast to detergent-suspended preparations, no CO-sensitive cytochrome b can be detected in the phospholipid-solubilized preparation or intact mitochondria. The half-reduction potential of cytochrome b₅₆₆ is pH-dependent above pH 7.0 (?60 mV/pH unit) while that of b₅₆₁ is essentially pH-independent from pH 6.7–8.5, in contrast to its pH dependence in intact mitochondria. EPR characterizations show the presence of three oxidized low-spin heme-iron signals with g values of 3.78, 3.41 and 3.37. The identification of these signals with cytochromes b₅₆₆ (b_T), b₅₆₁ (b_K) and c₁ respectively is made on the basis of redox midpoint potentials. No significant amounts of oxidized high-spin heme-iron are detectable. In addition, the preparation contains four distinct types of iron-sulfur centers: S₁ and S₂ (E_{m 7.4} = ?260 mV and 0 mV), and two iron-sulfur proteins which are associated with the cytochrome b-c₁ complex: Rieske's iron-sulfur protein (E_{m 7.4} = +280 mV) and Ohnishi's Center 5 (E_{m 7.4} = +35 mV).     

Shear stress and sediment resuspension in relation to submersed macrophyte biomass

We examined the impacts of macrophyte beds dominated by a canopy-forming (Myriophyllum sibiricum) and a meadow-forming (Chara canescens) species on bottom shear stress (τ) and resuspension in shallow Lake Christina, Minnesota (U.S.A.). Studies were conducted in late summer, 1998, when macrophyte biomass levels exceeded 200 g m^?2, and in early summer, 2000, when biomass was greatly reduced (<20 g m^?2) in both plant beds. The critical shear stress (τ_c) of sediments, measured experimentally in the laboratory, was low (1.4 dynes cm^?2) indicating potential for resuspension in the absence of macrophytes. During 1998, turbidity was low at the M. sibiricum and Chara station, rarely increasing when calculated bottom τ (calculated from wave theory assuming no biomass obstruction) exceeded τsub c sub, indicating that both beds reduced sediment resuspension at high biomass levels. In situτ (estimated τ), measured via gypsum sphere dissolution, did not exceed τ_c above the sediment interface in either bed during 1998. In contrast, sediment resuspension occurred in both beds during similar high winds in 2000. However, estimated τ was lower than calculated bottom τ, suggesting that at low biomass, macrophytes were having some impact on τ.     

Crystal structure and magnetic measurements of [Cr(en)3] [ZnCl4]Cl

The compound [Cr(en)₃][ZnCl₄]Cl has been synthesized by reaction of CrCl₃·6H₂O, Zn and [Cr(en)₃]₂(SO₄)₃ in HCl. Its molecular and crystalline structure was determined by X-ray diffraction methods, being monoclinic, P2₁/c, a=21.215(3), b=12.532(2), c=13.707(2) Å, β=95.21°, V= 3629(2) ų, D_x=1.738g cm⁻³, MW=474.9, Z= 8, F(000)=1928, λ(Mo Kα)=0.71069 Å, μ(Mo Kα)= 27.04 cm⁻¹, 288 K. No significant exchange interactions between Cr(III) cations in the crystalline lattice were found. Curie-Weiss behavior was found in the three directions tested (g₁=2.06±0.02,g₂= 2.08±0.02,g₃=2.09±0.01), T=1.2-1.4 K.     

Preparation,structure and properties of dicyano silver complexes of the M(en)3Ag2(CN)4 and M(en)2Ag2(CN)4 type

Complexes of the M(en)₃Ag₂(CN)₄ (M = Ni, Zn, Cd) and M(en)₂Ag₂(CN)₄ (M = Ni, Cu, Zn, Cd) type were prepared and identified by elemental analysis, infrared spectroscopy, measurement of magnetic susceptibility, and X-ray powder diffractometry. The crystal structures of Ni(en)₃Ag₂(CN)₄ (I) and Zn(en)₂Ag₂(CN)₄ (II) were determined by the method of monocrystal structure analysis. Complex I crystallizes in the space group C2/c, a = 1.2639(5), b = 1.3739(4), c = 1.2494(4) nm, β = 113.25(4)°, D_m = 1.86(1), D_c = 1.86 gcm⁻³ Z = 4, R = 0.0429. The crystal structure of I consists of complex cations [Ni(en)₃]²⁺ and complex anions [Ag(CN)₂]⁻. Complex II crystallizes in the space group I2/m, a = 0.9150(3), b = 1.3308(4), c = 0.6442(2) nm, β = 95.80(3)°, D_m = 2.14(1), D_c = 2.15 gcm⁻³, Z = 2, R = 0.0334. Its crystal structure consists of infinite, positively charged chains of the [-NCAgCNZn- (en)₂]_nⁿ⁺ type and isolated [Ag(CN)₂]⁻ anions. The atoms of Ag are positioned parallely to the z axis and the AgAg distance is equal to 0.3221(2) nm.     

Kinetics of the aerobic co-metabolism of 1,1-dichloroethylene by Achromobacter sp.: a novel benzene-grown culture

Batch experiments were performed for the aerobic co-metabolism of 1,1-dichloroethylene (1,1-DCE) by Achromobacter sp., identified by gene sequencing of 16S rRNA and grown on benzene. Kinetic models were employed to simulate the co-metabolic degradation of 1,1-DCE, and relevant parameters were obtained by non-linear least squares regression. Benzene at 90 mg L^?1 non-competitively inhibited degradation of 1,1-DCE (from 125 to 1,200 μg L^?1). The maximum specific utilization (k_c) rate and the half-saturation constant (K_c) for 1,1-DCE were 54 ± 0.85 μg h^?1 and 220 ± 6.8 μg L^?1, respectively; the k_b and K_b for benzene were 13 ± 0.18 mg h^?1 and 28 ± 0.42 mg L^?1, respectively. This study provides a theoretical basis to predict the natural attenuation when benzene and 1,1-DCE occur as co-contaminants.     

Quantifying measures to limit wind-driven resuspension of sediments for improvement of the ecological quality in some shallow Dutch lakes

Although phosphorus loadings are considered the main pressure for most shallow lakes, wind-driven resuspension can cause additional problems for these aquatic ecosystems. We quantified the potential effectiveness of measures to reduce the contribution of resuspended sediments, resulting from wind action, to the overall light attenuation for three comparable shallow peat lakes with poor ecological status in the Netherlands: Loosdrecht, Nieuwkoop, and Reeuwijk (1.8–2.7 m depth, 1.6–2.5 km fetch). These measures are: 1. wave reducing barriers, 2. water level fluctuations, 3. capping of the sediment with sand, and 4. combinations of above. Critical shear stress of the sediments for resuspension (V _crit), size distribution, and optical properties of the suspended material were quantified in the field (June 2009) and laboratory. Water quality monitoring data (2002–2009) showed that light attenuation by organic suspended matter in all lakes is high. Spatial modeling of the impact of these measures showed that in Lake Loosdrecht limiting wave action can have significant effects (reductions from 6% exceedance to 2% exceedance of V _crit), whereas in Lake Nieuwkoop and Lake Reeuwijk this is less effective. The depth distribution and shape of Lake Nieuwkoop and Lake Reeuwijk limit the role of wind-driven resuspension in the total suspended matter concentration. Although the lakes are similar in general appearance (origin, size, and depth range) measures suitable to improve their ecological status differ. This calls for care when defining the programme of measures to improve the ecological status of a specific lake based on experience from other lakes.     

Using chitosan-modified clays to control black-bloom-induced black suspended matter in Taihu Lake: Deposition and resuspension of black matter/clay flocs

A cyanobacteria-induced black bloom in Taihu Lake, 2007, subjected nearly one million Wuxi City residents to a drinking water crisis. This black bloom attracted wide attention in China and the rest of the world. However, black bloom is a highly weather-dependent event, and its rapid movement in lakes makes it difficult to predict where it will occur. Therefore, jar-tests and simulated flow experiments were performed to investigate the flocculation, deposition, and resuspension of black-bloom-induced black matter. At a dosage of 0.2 g L⁻¹ chitosan + 1 g L⁻¹ diatomite, 90% of the turbidity was removed within 1 h in jar-tests and in low flow speed simulated experiments. However, the black matter/clay flocs did not fully sink, and stratification of turbidity apparently occurred in the lower part of the tank during the simulated flow experiments. The resuspension experiments under simulated flow speeds showed that at a wind speed of 1–6 m s⁻¹ in Taihu Lake produced currents that did not greatly affect floc resuspension, but a wind speed of 3–4 m s⁻¹ produced waves that could induce floc resuspension. Quartz sand was sprayed over the flocs to verify its effect on inhibiting resuspension. A shear stress of 0.37 N m⁻² did not induce floc resuspension, which indicated that a wind speed of 6 m s⁻¹ would not induce floc resuspension in Taihu Lake.     

Sediment resuspension and light attenuation in Peoria Lake: can macrophytes improve water quality in this shallow system?

We examined sediment resuspension and light attenuation in relation to the potential for macrophytes to improve water quality conditions in Peoria Lake, Illinois (U.S.A.). The lake exhibited high total suspended solids (TSS) loading and retention of predominantly fine-grained particles in 2000. Large fetches along prevailing wind rose, coupled with shallow morphometry and sediment particles composed of >90% silt and clay resulted in frequent periods of sediment resuspension. As calculated (wave theory) shear stress increased above the critical shear stress (measured experimentally), turbidity increased substantially at a resuspension monitoring station. Resuspension model explorations suggested that establishment of submersed aquatic macrophytes could substantially reduce sediment resuspension in Peoria Lake. However, K _d is currently very high, while Secchi transparency low, at in-lake stations. Thus, in order to establish a persistent macrophyte population in the lake to control resuspension, the underwater light regime will have to improve quite dramatically.     

Studies on the orientations of the mitochondrial redox carriers. Orientation of the chromophores of cytochrome b--c1 complex with respect to the plane of a cytochrome b--c1 complex--lipid model membrane.

Orientations of the active site chromophores of the mitochondrial cytochrome b-c₁ complex incorporated into liposomes have been investigated in hydrated oriented multilayers of proteoliposome membranes using optical and epr spectroscopy. The hemes of cytochromes c₁ and b were found to be oriented with the normal to their heme planes lying approximately in the plane of the proteoliposome membrane. Rieske's iron-sulfur center was oriented with the z-axis of the g tensor parallel to the plane of the membranes. It is concluded that the cytochrome b-c₁ complex has a structural asymmetry which causes it to orient with respect to the lipid bilayer.