Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples.

Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed 17 Ryugu samples measuring 1 to 8 millimeters. Carbon dioxide-bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu's parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and calcium- and aluminum-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed through aqueous alteration reactions at low temperature, high pH, and water/rock ratios of <1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate that Ryugu's parent body formed ~2 million years after the beginning of Solar System formation.

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.

Thermal and impact histories of 25143 Itokawa recorded in Hayabusa particles.

Understanding the origin and evolution of near-Earth asteroids (NEAs) is an issue of scientific interest and practical importance because NEAs are potentially hazardous to the Earth. However, when and how NEAs formed and their evolutionary history remain enigmas. Here, we report the U-Pb systematics of Itokawa particles for the first time. Ion microprobe analyses of seven phosphate grains from a single particle provide an isochron age of 4.64 ± 0.18 billion years (1σ). This ancient phosphate age is thought to represent the thermal metamorphism of Itokawa's parent body, which is identical to that of typical LL chondrites. In addition, the incorporation of other particles suggests that a significant shock event might have occurred 1.51 ± 0.85 billion years ago (1σ), which is significantly different from the shock ages of 4.2 billion years of the majority of shocked LL chondrites and similar to that of the Chelyabinsk meteorite. Combining these data with recent Ar-Ar studies on particles from a different landing site, we conclude that a globally intense impact, possibly a catastrophic event, occurred ca. 1.4 Ga ago. This conclusion enables us to establish constraints on the timescale of asteroid disruption frequency, the validity of the crater chronology and the mean lifetime of small NEAs.

A new X-ray fluorescence spectroscopy for extraterrestrial materials using a muon beam.

The recent development of the intense pulsed muon source at J-PARC MUSE, Japan Proton Accelerator Research Complex/MUon Science Establishment (10(6) s(-1) for a momentum of 60 MeV/c), enabled us to pioneer a new frontier in analytical sciences. Here, we report a non-destructive elemental analysis using µ(-) capture. Controlling muon momentum from 32.5 to 57.5 MeV/c, we successfully demonstrate a depth-profile analysis of light elements (B, C, N, and O) from several mm-thick layered materials and non-destructive bulk analyses of meteorites containing organic materials. Muon beam analysis, enabling a bulk analysis of light to heavy elements without severe radioactivation, is a unique analytical method complementary to other non-destructive analyses. Furthermore, this technology can be used as a powerful tool to identify the content and distribution of organic components in future asteroidal return samples.

Neutron activation analysis of a particle returned from asteroid Itokawa.

A single grain (~3 micrograms) returned by the Hayabusa spacecraft was analyzed by neutron activation analysis. This grain is mainly composed of olivine with minor amounts of plagioclase, troilite, and metal. Our results establish that the Itokawa sample has similar chemical characteristics (iron/scandium and nickel/cobalt ratios) to chondrites, confirming that this grain is extraterrestrial in origin and has primitive chemical compositions. Estimated iridium/nickel and iridium/cobalt ratios for metal in the Itokawa samples are about five times lower than CI carbonaceous chondrite values. A similar depletion of iridium was observed in chondrule metals of ordinary chondrites. These metals must have condensed from the nebular where refractory siderophile elements already condensed and were segregated.

[Meteoritics and mineralogy on possible ancient Martian life].

Possible relic biogenic activity in martian meteorite ALH84001 was proposed by McKay et al. (Science, 273, 924-930, 1996). This ancient meteorite of 4.5 billion years old contains abundant carbonates as secondary minerals precipitated from a fluid on the martian surface. They showed the following lines of evidence for the ancient life; (1) unique mineral compositions and biominerals, (2) polycyclic aromatic hydrocarbons (PAHs) in association with the carbonates, and (3) unique structures and morphologies typical of nanobacteria or microfossils. This review is divided into two parts; one is on the martian meteorites in general and ALH84001, which has many features unlike other martian meteorites, and the other is on mineralogical (biomineralogical) and geochemical features of the carbonates and microfossil-like structures. There is little doubt that ALH84001 is from Mars as well as eleven other SNC meteorites. However, the mineralogical and biomineralogical evidence for martian bacteria given by McKay et al. (1996) is controversial, and could be formed by non-biogenic processes. Thus, further study of ALH84001 and other martian meteorites is required. We also need to consider the future Mars mission especially sample return mission.

A case of carbamylphosphate synthetase-I deficiency associated with secondary carnitine deficiency--L-carnitine treatment of CPS-I deficiency.

We describe a male infant with congenital hyperammonaemia due to partial carbamylphosphate synthetase-I (CPS-I) deficiency. At 21 days of age, he had convulsions and at 53 days of age hyperammonaemic coma. Therapy with sodium benzoate, L-arginine, essential amino acids, L-carnitine and peritoneal dialysis lowered the blood ammonia levels, and his clinical manifestations improved. The CPS-I activity in liver tissue obtained by open biopsy was about 25.6% of normal values. The serum and urine free carnitine levels in the patient decreased during the hyperammonaemic crisis and were low at 7 months of age. After oral administration of L-carnitine (10 mg/kg per day) at 7 months of age, the mean blood ammonia levels decreased significantly, accompanied by an increase in serum and urine free carnitine levels. We propose the use of L-carnitine therapy to prevent secondary carnitine deficiency in patients with CPS-I deficiency as well as ornithine transcarbamylase (OTC) deficiency.

The role of amino acids and their transport systems in the regulation of ureogenesis in the primary culture of adult rat hepatocytes.

The biosynthesis of urea, the metabolism of ammonia and the transport of amino acids were studied using the primary culture of hepatocytes from adult rats. The urea synthesis and ammonia detoxication were affected by the amino acids of urea cycle intermediates, such as ornithine, arginine and aspartate. When the hepatocytes were incubated in the medium containing 1 mM ammonium chloride, the transport activity of system-A, which was determined by the uptake of specific substrate methyl-2-amino isobutyric acid (MeAIB), did not change compared with the control level. However, the transport activity of ornithine was increased to a maximum after 4 hr of incubation with ammonia, and then decreased gradually to twice the control level. The activity of ornithine transcarbamylase (OTC) increased to twice the control. These results indicated that the amino acids of urea cycle intermediates, especially ornithine, can be the important regulators of ureogenesis.

Neonatal hyperammonemia associated with carnitine deficiency.

We report a case of neonatal hyperammonemia associated with secondary carnitine deficiency. She suffered from hyperammonemia soon after the birth, and then presented severe metabolic acidosis at 2 months of age. She was successfully treated for acidosis with oral administration of L-carnitine (100 mg/kg/day). Since hyperammonemia recurred with the increase of protein intake, it was necessary to increase the dose of carnitine to 150 mg/kg/day. Urea cycle enzymopathies were excluded from the laboratory data. The urinary organic acid profiled by gas chromatography mass spectrometry revealed no abnormalities. It was found that the carnitine contents in serum urine and muscle were decreased. After we investigated the carnitine status in other members of the family, the brother of this patient, who had died of metabolic acidosis and hyperammonemia of unknown etiology in the neonatal period, was also revealed to have carnitine deficiency. Since specific enzyme defects which caused secondary carnitine deficiency could not be detected in our patients, further biochemical characterization would be necessary to clarify the cause of hyperammonemia.

Studies on the expression of liver-specific functions of human fetal hepatocytes in primary culture.

Biochemical functions of human livers were studied using fetal hepatocytes in primary culture. Immunocytochemical staining showed that albumin was not expressed in any fetal hepatocytes, whereas alpha-fetoprotein was detected in almost all the cells. Tryptophan 2,3-dioxygenase (TO, EC 1.13.11.11.) activity was not induced in the presence of 10(-7) M dexamethasone and 10(-7) M glucagon, but the activity of tyrosine aminotransferase (TAT, EC 2.6.1.5.) was elevated about 35 fold under the same conditions. These results suggest that the TAT and alpha-fetoprotein genes are activated in human fetal liver at 14 to 20 weeks of gestation.

Immunoenzymatic studies of ornithine transcarbamylase (OTC) in liver of patients with OTC deficiency by enzyme linked immunosorbent assay (ELISA).

Antigen contents of ornithine transcarbamylase (OTC) protein in the liver of 5 patients with OTC deficiency and mutant mice were studied by ELISA. OTC activities in the liver tissues of 2 patients were 13.1% and 5.2% of the controls, respectively. The 2 patients' antigen contents of OTC protein were decreased in parallel with the enzyme activities. OTC antigen contents were not detected in the liver tissues of remaining 3 patients who had the complete type of OTC deficiency. Enzyme activities, kinetic properties and antigen contents of the OTC deficient mutant mice were the same as the results reported previously (Briand et al. 1982). The ELISA method for the assay of OTC antigen contents used in this study is more sensitive as compared with the radial immunodiffusion technique.

Control of growth and amino acid transport of mature rat hepatocytes by human newborn serum.

DNA synthesis and system A-mediated amino acid transport were studied in primary culture of adult rat hepatocytes maintained as a monolayer. Potent growth promoting activity and inducibility of system A-mediated amino acid transport could be found in human newborn sera but not in human adult sera. The maximal activity to promote DNA synthesis was about the same level as insulin (10(-7) M) plus epidermal growth factor (EGF, 20 ng/ml). These results suggest the presence of a hepatocyte-specific growth factor in human newborn sera controlling the amino acid metabolism during the newborn period.

Cytotoxicities of sodium benzoate in primary culture of hepatocytes from adult rat liver.

The cytotoxicities of sodium benzoate was studied using primary culture of hepatocytes established from adult rat liver by a collagenase perfusion technique and maintained as a monolayer in serum-free culture medium. The activities of ornithine transcarbamylase (as a marker of mitochondria) and tyrosine aminotransferase (as a marker of cytosol) were clearly suppressed by sodium benzoate at concentration in excess of 500 micrograms/ml. Intracellular protein synthesis and DNA synthesis were also suppressed, and the suppression of DNA synthesis was observed even with a lower concentration of benzoate (100 micrograms/ml).

Clinical, biochemical and enzymatic studies in type I hyperprolinemia associated with chromosomal abnormality.

A severe mentally retarded infant with type I hyperprolinemia associated with chromosomal abnormality is reported. The patient had a characteristic facial appearance of hyperprolinemia and suffered from convulsions after the age of 10 months. The child developed severe mental and motor retardation. The karyotype of the patient revealed partial duplication of the short arm in chromosome 10 using G banding techniques. The patient and her mother showed a fasting hyperprolinemia and an abnormal clearance curve after the proline load in the serum. The proline oxidase activities of the liver tissues obtained by biopsy in the patient was about 9% of those of controls. Kinetic studies and mixed experiments of the enzyme were with normal limits. Restriction of dietary proline at the age of 12 months revealed a prompt fall of the plasma levels of proline to the normal range, and a low proline diet was continued until the present time. During the period of dietary treatment, growth was satisfactory, but her mental development did not improve. From the developmental patterns of proline oxidase activities postnataldy, we speculated that restriction of dietary proline intake should be relieved with age.

Citrullinemia: quantitative deficiency of argininosuccinate synthetase in the liver.

Two cases of citrullinemia were reported. Case 1 was an one month old female. Her clinical course and findings were different from the fulminant type of neonatal citrullinemia reported in predominantly Caucasian countries. Our patient was well controlled under a low protein diet and essential amino acids till 9 months of age, but unfortunately she died of Reye's like syndrome. Case 2 was 31 year old male (at the time of death). He was admitted to our hospital because of hyperammonemia and mental retardation. By subsequent laboratory investigations he was diagnosed as having adult type of citrullinemia and died of hepatoma. Enzymological analysis revealed that argininosuccinate synthetase (ASS) activities in the liver tissues of the patients decreased to 40% (Case 1), 20% (Case 2) compared with those in control liver tissues. The other urea cycle enzyme activities were all within normal range. ASS activities in the kidney and brains of the two cases were within normal range. The kinetic constant values of ASS for three substrates in the tissues of liver and kidney were all normal. Results of immunochemical analyses indicated that citrullinemia in our patients was caused by a quantitative deficiency of ASS associated proteins of the liver and kidney tissues as to the molecular weight.