Pebbles and sand on asteroid (162173) Ryugu: In situ observation and particles returned to Earth.

The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu's boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid.

An artificial impact on the asteroid (162173) Ryugu formed a crater in the gravity-dominated regime.

The Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble-pile structure. We describe an impact experiment on Ryugu using Hayabusa2's Small Carry-on Impactor. The impact produced an artificial crater with a diameter >10 meters, which has a semicircular shape, an elevated rim, and a central pit. Images of the impact and resulting ejecta were recorded by the Deployable CAMera 3 for >8 minutes, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface. The ejecta curtain was asymmetric and heterogeneous and it never fully detached from the surface. The crater formed in the gravity-dominated regime; in other words, crater growth was limited by gravity not surface strength. We discuss implications for Ryugu's surface age.

Sample collection from asteroid (162173) Ryugu by Hayabusa2: Implications for surface evolution.

The near-Earth asteroid (162173) Ryugu is thought to be a primitive carbonaceous object that contains hydrated minerals and organic molecules. We report sample collection from Ryugu's surface by the Hayabusa2 spacecraft on 21 February 2019. Touchdown images and global observations of surface colors are used to investigate the stratigraphy of the surface around the sample location and across Ryugu. Latitudinal color variations suggest the reddening of exposed surface material by solar heating and/or space weathering. Immediately after touchdown, Hayabusa2's thrusters disturbed dark, fine grains that originate from the redder materials. The stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time. We suggest that Ryugu previously experienced an orbital excursion near the Sun.

The surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy.

The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. We report reflectance spectra of Ryugu's surface acquired with the Near-Infrared Spectrometer (NIRS3) on Hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, which is consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu-A spinning top-shaped rubble pile.

The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate "spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.

The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes.

The near-Earth carbonaceous asteroid 162173 Ryugu is thought to have been produced from a parent body that contained water ice and organic molecules. The Hayabusa2 spacecraft has obtained global multicolor images of Ryugu. Geomorphological features present include a circum-equatorial ridge, east-west dichotomy, high boulder abundances across the entire surface, and impact craters. Age estimates from the craters indicate a resurfacing age of [Formula: see text] years for the top 1-meter layer. Ryugu is among the darkest known bodies in the Solar System. The high abundance and spectral properties of boulders are consistent with moderately dehydrated materials, analogous to thermally metamorphosed meteorites found on Earth. The general uniformity in color across Ryugu's surface supports partial dehydration due to internal heating of the asteroid's parent body.

Images from the surface of asteroid Ryugu show rocks similar to carbonaceous chondrite meteorites.

The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu's surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.

Dispersion state of phospholipids and fluorescence production with peroxidation in organic solvents: investigated by time-resolved fluorescence technique.

Fluorescent substances were found to be produced efficiently when phospholipids containing phosphatidylethanolamine (PE) and linoleic chains were autoxidized in non-polar solvents. By using these fluorescent substances as intrinsic probes, the dispersion state of phospholipids was investigated in various organic solvents. Fluorescence anisotropy decay measurements indicated that the aggregation size of phospholipids was much larger in hexane than in chloroform, methanol and tert-butyl alcohol. The average diameter of phospholipid aggregates in hexane was calculated to be 4-6 nm, which was dependent on the lipid composition. A consistent result was obtained when N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn-gly cer o-3- phosphoethanolamine (NBD-PE) was used as an extrinsic probe. Comparison of the fluorescence data with small-angle X-ray scattering (SAXS) data suggested that a reverse micellar structure of phospholipids formed in hexane. It was shown that phospholipid aggregation enhanced the extent of peroxidation as well as the production yield of fluorescent substances of phospholipid.

Fluorescence energy transfer studies of transmembrane location of retinal in purple membrane.

A diffusion-enhanced energy transfer technique was employed for the determination of transmembrane location of the retinal chromophore in the purple membrane. Theoretical considerations showed that the rate of energy transfer from an energy donor embedded within a membrane to acceptors dissolved in solvent could be described by an analytical function of the distance a of closest approach between the donor and acceptor, if the "rapid-diffusion limit" was attained. The criterion for this limit was given by the relation: (RO)6 much less than 20D tau Da4, where RO is the characteristic distance of energy transfer, D is the diffusion coefficient of the acceptor and tau D is the fluorescence lifetime of the donor in the absence of acceptor. By photo-reduction of the purple membrane with sodium borohydride, the retinal chromophore was converted to a highly fluorescent derivative, which showed a broad emission band in the visible region. From analysis of the fluorescence decay curves of the photo-reduced purple membrane in the presence of various concentrations of cobalt-ethylenediamine tetraacetate (Co-EDTA: energy acceptor), the depth of the chromophore from the membrane surface was estimated to be 8 (+/-3) A. This result was supported by investigations of energy transfer processes in a system where the native purple membranes and the photo-reduced membranes were stacked in parallel: the energy acceptor in this system was the native retinal chromophore.

Polyhedral assembly of a membrane protein in its three-dimensional crystal.

A novel ordered assemblage of bacteriorhodopsin, a transmembrane protein functioning as a light-driven proton pump, is found in its three-dimensional crystal. Atomic force microscope images of the crystal surface reveal that spherical protein clusters with a diameter of approximately 50 nm are hexagonally close-packed. Electron micrographs of mechanically disintegrated crystals show that the inside of the protein cluster is filled with the mother liquor. The crystal is made up of hollow protein clusters. When disintegrated crystals are illuminated in the presence of a lipophilic anion, a significant alkalization of the external medium occurs. This result indicates that the protein cluster contains native lipids and that the cytoplasmic side of the protein faces the external medium. X-ray diffraction patterns and the observed diameter of the spherical shell suggest that approximately 200 bacteriorhodopsin trimers are aligned on a polyhedral surface lattice. Another remarkable feature of the spherical assemblies of bacteriorhodopsin is that they fuse with each other at low ionic strength and occasionally form a tubular or doughnut-like structure. The concept of membrane protein polymorphism is introduced on the basis of these observations, and it is used to describe the dynamic structure of some other biological membranes.

A novel three-dimensional crystal of bacteriorhodopsin obtained by successive fusion of the vesicular assemblies.

When the two-dimensional crystal of bacteriorhodopsin (bR), purple membrane, is incubated at high temperature (32 degreesC) with a small amount of the neutral detergent octylthioglucoside in the presence of the precipitant ammonium sulfate, a large fraction of the membrane fragments is converted into spherical vesicles with a diameter of 50 nm, which are able to assemble into optically isotropic hexagonal crystals when the precipitant concentration is increased. The vesicularization of purple membrane takes place under such a condition that the miscibility of the detergent to the aqueous phase becomes very low, and we suggest that it is initiated by insertion of the detergent molecules into the membrane. At low temperature, the transformation into the vesicular structure is inhibited and no large crystal is produced directly from membrane/detergent/precipitant mixtures. When a suspension of the spherical vesicles produced at the high temperature is cooled and concentrated below 15 degreesC, however, a birefringent hexagonal crystal is produced that diffracts X-rays beyond 2.5 A resolution. This new crystal belongs to the space group P622 with unit cell dimensions of a=b=104.7 A and c=114.1 A, and it is shown to be made up of stacked planar membranes, in each of which the bR trimers are arranged on a honeycomb lattice and the space among the proteins is filled with the detergent molecules and native lipids. These stacked membranes are suggested to be produced by successive fusion of the spherical vesicles. This implies that the crystallization is achieved without any step for complete solubilization of the protein. The present result offers a unique crystallization method that may be applicable to such membrane proteins that are liable to denature in the presence of an excess amount of detergent.

Molecular structural studies of effector functions of a mouse immunoglobulin G that lacks the entire CH1 domain: small-angle X-ray scattering, nanosecond fluorescence depolarization and stable isotope-aided NMR analyses.

Molecular structural studies are reported of a short-chain mouse IgG2a antibody that lacks the entire CH1 domain. We have recently shown that (1) this short-chain antibody comprises two components in which the inter light-chain disulfide bridge does and does not exist, and (2) these two components are different in the constitutive complement-activating activity [Mizutani et al. (1993) J. Immunol. 150, 131-138]. Structures were compared for these two components on the basis of small-angle X-ray scattering, nanosecond fluorescence depolarization and isotope-aided NMR data. It has been discussed how the presence and absence of the inter light-chain disulfide bridges affect the complement-activating activity of the two components of the short-chain antibody.

Highly selective separation of rhodopsin from bovine rod outer segment membranes using combination of divalent cation and alkyl(thio)glucoside.

The micellization process of bovine rod outer segment (ROS) membranes is investigated utilizing a series of neutral detergents. It is found that when alkyl(thio)glucosides with an appropriate hydrophillic-lipophilic balance (e.g. octylthioglucoside) are used in combination with a divalent cation, rhodopsin is selectively extracted from ROS membranes at a specific detergent-to-membrane ratio. This allows remarkable purification of rhodopsin by a single-step solubilization, because the residual membranes are heavily aggregated in the presence of divalent cation and are therefore easily sedimented by low-speed centrifugation. The absorption spectrum of the supernatant reproducibly exhibits an A280/A500 value of 1.6, an excellent value that could rarely be obtained by chromatographic purification. The degree of purification also depends on the type of divalent cation included in the solubilization solution; specific binding of IIB-series cations (Zn2+ and Cd2+) to ROS membranes is suggested to play an important role in the solubilization process. The present result represents a unique example of selective solubilization of a specific membrane protein from highly aggregated membranes.

Significance of amino groups of phosphatidylethanolamine in phospholipid peroxidation of mixed liposomes.

The effect of distribution of phosphatidylethanolamine (PE) in multilamellar vesicles (MLV) on their peroxidative susceptibility was studied. Liposomes containing various ratios of L-alpha-dilinoleoyl phosphatidylcholine (DiLinPC) and L-alpha-dilinoleoyl phosphatidylethanolamine (DiLinPE) were peroxidized by ferrous ion or a water-soluble radical initiator 2,2'-azobis (2-amidino-propane) dihydrochloride (AAPH). The oxygen consumption rate was compared with the formation kinetics of fluorescent products. Inclusion of PE in liposomes was found to accelerate the Fe(2+)-dependent peroxidation. Modification of the amino group of PE with 2,4,6-trinitrobenzenesulfonic acid (TNBS) inhibited Fe(2+)-induced oxygen consumption in the late stage where fluorescent substances formed. A possible role of the amino group of PE on lipid peroxidation is discussed, especially in terms of its reactivity with oxidation products and subsequent formation of fluorescent substances.

Time resolved study of effect of chlorpromazine on mobility of cytochrome P-450 and phospholipids in the inner membrane of adrenocortical mitochondria.

The effects of chlorpromazine on the mobility of cytochrome P-450 and the fluidity of lipid membranes have been investigated in bovine adrenocortical submitochondrial particles (SMP). Rotational diffusion of the cytochrome was measured by observing the decay of absorption anisotropy, ra(t), after photolysis of the heme.CO complex by a vertically polarized laser flash. Analysis of ra(t) was based on a 'rotation-about-membrane-normal' model. The anisotropy decayed within 2 ms to a time independent value r3. The presence of chlorpromazine decreased the mobile population of cytochrome P-450 from 28 to 23%. The rotational relaxation time phi a of the mobile population (approximately 1100 microseconds) was, however, not significantly changed by chlorpromazine. The lipid fluidity was examined by observing time-resolved fluorescence anisotropy, rf(t), of 1,6-diphenyl 1,3,5-hexatriene (DPH). The anisotropy rf(t) decayed within 70 ns to a time independent value r infinity. The motion of DPH was analyzed based on a 'wobbling-in-cone' model. The presence of chlorpromazine decreased the cone angle from 42 degrees to 39 degrees, while the rotational relaxation time phi f (approximately 2 ns) was not significantly changed by the presence of chlorpromazine. These results demonstrate that chlorpromazine decreased the mobility of not only lipids but also membrane proteins.

Value of thallium-201 early reinjection for assessment of myocardial viability.

To assess the efficacy of early reinjection for predicting post intervention improvement in thallium-201 (T1) uptake and regional wall motion, we reinjected a small dose of T1 following post-stress imaging and obtained reinjection early images (10 min after early reinjection) and reinjection delayed images (3 hr afterwards) in 40 patients who were referred to us for revascularization (group I). Twenty-nine patients in group I also underwent conventional stress-redistribution T1 scintigraphy (group II). Conventional stress-redistribution T1 scintigraphy was repeated after intervention. Contrast left ventriculography was performed before and after intervention and changes in regional wall motion were assessed in 22 of 40 patients. In group I, the predictive value for improvement and no improvement (the accuracy) of reinjection early images in perfusion was 83%, while that of reinjection delayed images was 91%. Furthermore, the accuracy of reinjection early images in regional wall motion was 80%, while it was 91% for reinjection delayed images. In group II, the accuracy in perfusion was 78% and the value in regional wall motion was 70%. Both accuracy in perfusion and in regional wall motion obtained from reinjection delayed images were significantly higher than the values in group II (p < 0.05). These data suggest that early reinjection is useful for predicting postintervention thallium uptake and regional wall motion.