Unique rearrangement of ergocalciferol side chain in vitro: production of a biologically highly active homologue of 1,25-dihydroxyvitamin D3

In vitro incubation of 24-epi-25-hydroxyvitamin D2 with chicken kidney homogenate produced several compounds, one of which had an affinity equal to that of 1,25-dihydroxyvitamin D2 for the chick intestinal receptor. The affinity of 24-epi-1,25-dihydroxyvitamin D2 for the same receptor was found to be half that of 1,25-dihydroxyvitamin D2. The unknown compound was produced only when homogenate was prepared from pooled kidneys taken from both vitamin D deficient and replete chickens. The compound has been tentatively identified as 1,25-dihydroxy-22-dehydro-26-homovitamin D3 by ultraviolet absorption spectrophotometry and mass spectrometry. Chemical synthesis of 1,25-dihydroxy-22-dehydro-26-homovitamin D3 provided additional evidence for the structure. Administration of this 26-homologue of 1,25-dihydroxyvitamin D3 at the dose level of 650 pmol/rat stimulated bone calcium mobilization in the hypocalcemic rat equal to that of 1,25-dihydroxyvitamin D3. Thus, this paper demonstrates unique methyl migration on the side chain of 24-epi-1,25-dihydroxyvitamin D3 to form a more biologically potent analogue.     

Sodium and Chloride Ion-Dependent Transport of β-Alanine Across the Blood-Brain Barrier

Abstract: The characteristics of β-alanine transport at the blood-brain barrier were studied by using primary cultured bovine brain capillary endothelial cells. Kinetic analysis of the β-[³H]alanine transport indicated that the transporter for β-alanine functions with K_t of 25.3 ± 2.5 µ M and J _max of 6.90 ± 0.48 nmol/30 min/mg of protein in the brain capillary endothelial cells. β-[³H]Alanine uptake is mediated by an active transporter, because metabolic inhibitors (2,4-dinitrophenol and NaN₃) and low temperature reduced the uptake significantly. Furthermore, the uptake of β-[³H]alanine required Na⁺ and Cl⁻ in the external medium. Stoichiometric analysis of the transport demonstrated that two sodium ions and one chloride ion are associated with one β-alanine molecule. The Na⁺ and Cl⁻-dependent uptake of β-[³H]alanine was stimulated by a valinomycin-induced inside-negative K⁺-diffusion potential. β-Amino acids (β-alanine, taurine, and hypotaurine) inhibited strongly the uptake of β-[³H]alanine, whereas α- and γ-amino acids had little or no inhibitory effect. In ATP-depleted cells, the uptake of β-[³H]alanine was stimulated by preloading of β-alanine or taurine but not l -leucine. These results show that β-alanine is taken up by brain capillary endothelial cells, via the secondary active transport mechanism that is common to β-amino acids.     

白额鹱卵壳的扫描电镜观察

本文报道白额鹱卵壳的壳膜、孔锥层、海绵层、表层等的超微结构,并对卵壳元素进行ＴＮ－５５００能谱分析。     

Enhancement of DNA polymerase II activity in E. coli after treatment with N-methyl-N'-nitro-N-nitrosoguanidine.

The G₁(G₀) arrest induced in NRK cells by picolinic acid was preceded by marked changes in iron metabolism. In contrast, picolinic acid did not significantly prevent zinc uptake and changes in intracellular zinc were small and clearly preceded by changes in iron. A kinetic study revealed that iron uptake by NRK cells was rapidly halted by picolinic acid. Experiments with radioiron-labeled cells indicated that picolinic acid, in a dose dependent manner, effectively removed iron from the cells. The dose of picolinic acid that exactly removed iron from the cells was also the concentration that induced the G₁(G₀) arrest. Picolinic acid, therefore, may induce the growth inhibition by selectively withholding iron from the cells. These data strongly suggest that iron availability may be a controlling factor in the initiation of DNA synthesis in NRK cells.     

Isolation of the diterpenoid teuflin (6-epiteucvin) from Teucrium viscidum var. miquelianum

The diterpenoid teuflin (6-epiteuevin) has been isolated from Teucrium viscidum var. miquelianum. Its base catalysed epimerization into teucvidin was studied under mild conditions and the pathway is discussed.     

Configuration of PKCα-C2 Domain Bound to Mixed SOPC/SOPS Lipid Monolayers

X-ray reflectivity measurements are used to determine the configuration of the C2 domain of protein kinase Cα (PKCα-C2) bound to a lipid monolayer of a 7:3 mixture of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine and 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoserine supported on a buffered aqueous solution. The reflectivity is analyzed in terms of the known crystallographic structure of PKCα-C2 and a slab model representation of the lipid layer. The configuration of lipid-bound PKCα-C2 is described by two angles that define its orientation, θ = 35° ± 10° and φ =210° ± 30°, and a penetration depth (=7.5 ± 2 Å) into the lipid layer. In this structure, the β-sheets of PKCα-C2 are nearly perpendicular to the lipid layer and the domain penetrates into the headgroup region of the lipid layer, but not into the tailgroup region. This configuration of PKCα-C2 determined by our x-ray reflectivity is consistent with many previous findings, particularly mutational studies, and also provides what we believe is new molecular insight into the mechanism of PKCα enzyme activation. Our analysis method, which allows us to test all possible protein orientations, shows that our data cannot be explained by a protein that is orientated parallel to the membrane, as suggested by earlier work.     

Epidemiological,Clinical and Serological Characteristics of Children with Coronavirus Disease 2019 in Wuhan: A Single-centered,Retrospective Study

In December 2019, SARS-CoV-2 was first detected in the samples obtained from three adult patients who suffered from an unknown viral pneumonia in Wuhan (Li et al. 2020). This unknown viral pneumonia is further named as coronavirus disease 2019 (COVID-19) by the World Health Organization. To date, the number of new COVID-19 cases has continued to skyrocket and the impact of SARS-CoV-2 on humans is far greater than any pathogen of this century in both breadth and depth. Previous studies have shown that adults with COVID-19 have symptoms of fever, dry cough, dyspnea, fatigue and lymphocytopenia. Moreover, COVID-19 is more likely to cause death in the elderly, especially those with chronic comorbidities (Huang et al. 2020). In Wuhan, more than 50, 000 COVID-19 cases have been confirmed, including over 780 pediatric patients, and only one child death case (Lu et al. 2020). Although the number of children cases was far fewer than that of adults, COVID-19 might endanger children's health and the information on children remains limited, especially in serological study. In the retrospective study, the investigators analyzed the epidemiological, clinical and serological characteristics of children with COVID-19 in Wuhan in the early stages of the outbreak, which might provide theoretical and practical help in controlling COVID-19 and similar emerging infectious diseases in the future.     

Integrative structure and function of the yeast exocyst complex

Exocyst is an evolutionarily conserved hetero‐octameric tethering complex that plays a variety of roles in membrane trafficking, including exocytosis, endocytosis, autophagy, cell polarization, cytokinesis, pathogen invasion, and metastasis. Exocyst serves as a platform for interactions between the Rab, Rho, and Ral small GTPases, SNARE proteins, and Sec1/Munc18 regulators that coordinate spatial and temporal fidelity of membrane fusion. However, its mechanism is poorly described at the molecular level. Here, we determine the molecular architecture of the yeast exocyst complex by an integrative approach, based on a 3D density map from negative‐stain electron microscopy (EM) at ~16 Å resolution, 434 disuccinimidyl suberate and 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride cross‐links from chemical‐crosslinking mass spectrometry, and partial atomic models of the eight subunits. The integrative structure is validated by a previously determined cryo‐EM structure, cross‐links, and distances from in vivo fluorescence microscopy. Our subunit configuration is consistent with the cryo‐EM structure, except for Sec5. While not observed in the cryo‐EM map, the integrative model localizes the N‐terminal half of Sec3 near the Sec6 subunit. Limited proteolysis experiments suggest that the conformation of Exo70 is dynamic, which may have functional implications for SNARE and membrane interactions. This study illustrates how integrative modeling based on varied low‐resolution structural data can inform biologically relevant hypotheses, even in the absence of high‐resolution data.