猪胰脏中胰岛素拮抗肽的分离纯化及其性质的初步研究

从猪胰脏的酸醇提取液中纯化了一个新的活性多肽——胰岛素拮抗肽,它在整体和细胞水平上对胰岛素都有明显的拮抗作用。猪胰脏的酸醇提取液经CM-52、BioGel P-6、DEAE-52及RP-HPLC纯化后,可得到纯的胰岛素拮抗肽。它能剂量相关地抑制胰岛素在离体大鼠脂肪细胞中的促脂合成活性,抑制50％胰岛素活性时所需的胰岛素拮抗肽为2.0×10~(-10)mol/L与被拮抗的胰岛素剂量在同一水平上。该肽含有较多的碱性氨基酸,分子量的3 000,其N-末端是封闭的。胰岛素拮抗肽的上述理化特征及其对胰岛素的拮抗活性均不同于目前已知的胰脏活性多肽。它对脂肪细胞中胰岛素的拮抗作用可能具有重要的生理意义。     

Freezing of phosphocholine headgroup in fully hydrated sphingomyelin bilayers and its effect on the dynamics of nonfreezable water at subzero temperatures.

Differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spectroscopy are applied to characterize the nonfreezable water molecules in fully hydrated D2O/sphingomyelin at temperatures below 0 degrees C. Upon cooling, DSC thermogram displays two thermal transitions peaked at -11 and -34 degrees C. The high-temperature exothermic transition corresponds to the freezing of the bulk D2O, and the low-temperature transition, which has not previously been reported, can be ascribed to the freezing of the phosphocholine headgroup in the lipid bilayer. The dynamics of nonfreezable water are also studied by 2H NMR T1 (spin-lattice relaxation time) and T2e (spin-spin relaxation time obtained by two pulse echo) measurements at 30.7 MHz and at temperatures down to -110 degrees C. The temperature dependence of the T1 relaxation time is characterized by a distinct minimum value of 2.1 +/- 0.1 ms at -30 degrees C. T2e is discontinuous at temperature around -70 degrees C, indicating another freezing-like event for the bound water at this temperature. Analysis of the relaxation data suggest that nonfreezable water undergoes both fast and slow motions at characteristic NMR time scales. The slow motions are affected when the lipid headgroup freezes.     

Immunohistochemical distribution of MAM-3 and MAM-6 antigens in developing salivary glands of the human fetus

Summary The immunohistochemical expression of MAM-3 and MAM-6 antigens was studied in developing human fetal salivary gland removed at autopsy of 22 normal fetuses of varying maturity (10–40 weeks of gestation). The onset of functional maturation in the fetal gland was seen at 21 weeks of gestational maturity. The acini and ducts then underwent distinct alterations in antigen expression with growth and maturation until the late developmental stage (33–40 weeks of gestation) when they resemble the adult salivary gland. The role of maturing duct cells in histogenesis of salivary gland tumours is discussed.     

元谋新第三纪食肉动物化石的初步观察

本文对云南元谋盆地产古猿化石地点的部分食肉类化石进行了初步观察分类,认为它们的时代似应稍晚于禄丰,相当上新世早期,估计距今5-6百万年.     

Effects of excess selenomethionine on selenium status indicators in pregnant long-tailed macaques (Macaca fascicularis)

Forty pregnant long-tailed macaques were treated daily for 30 d with 0, 25, 150 or 300 μg selenium as L-selenomethionine/kg body weight. Erythrocyte and plasma selenium and glutathione peroxidase specific activities, hair and fecal selenium, and urinary selenium excretion were increased by and were linearly related to L-selenomethionine dose. Hair selenium was most sensitive to L-selenomethionine dose, with an 84-fold increase in the 300 μg selenium/(kg-d) group relative to controls (r=0.917). Daily urinary selenium excretion (80-fold,r=0.958), plasma selenium (22-fold,r=0.885), erythrocyte selenium (24-fold,r=0.920), and fecal selenium (18-fold,r=0.911) also responded strongly to L-selenomethionine. Erythrocyte and plasma glutathione peroxidase specific activities increased 154% and 69% over controls, respectively. Toxicity was associated with erythrocyte selenium >2.3 μg/mL, plasma selenium >2.8 μg/mL, and hair selenium >27 μg/g. Plasma, erythrocyte, and hair selenium concentrations may be useful for monitoring and preventing the toxicity of L-selenomethionine administered to humans in cancer chemoprevention trials.     

Isolation and Identification of Vesicular-Arbuscular Mycorrhiza-Stimulatory Compounds from Clover (Trifolium repens) Roots

Two isoflavonoids isolated from clover roots grown under phosphate stress were characterized as formononetin (7-hydroxy,4′-methoxy isoflavone) and biochanin A (5,7-dihydroxy,4′-methoxy isoflavone). At 5 ppm, these compounds stimulated hyphal growth in vitro and root colonization of an undescribed vesicular-arbuscular mycorrhiza, a Glomus sp. (INVAM-112). The permethylated products of the two compounds were inactive. These findings suggest that the isoflavonoids studied may act as signal molecules in vesicular-arbuscular mycorrhiza symbiosis.     

Biophysical correlates of lysophosphatidylcholine- and ethanol-mediated shape transformation and hemolysis of human erythrocytes. Membrane viscoelasticity and NMR measurement

The effects of monopalmitoylphosphatidylcholine (MPPC or lysophosphatidylcholine) and a series of short-chain primary alcohols (ethanol, 1-butanol and 1-hexanol) on cell shape, hemolysis, viscoelastic properties and membrane lipid packing of human red blood cells (RBCs) were studied. For MPPC, the effective membrane concentration to induce the formation of stage 3 echinocytes (8 x 10(6) molecules per cell) was one order of magnitude lower than that needed to induce 50% hemolysis (7 x 10(7) molecules per cell). In contrast, short-chain alcohols induced both shape changes and hemolysis within close concentration range (2.5 x 10(8) to 3.5 x 10(8) molecules per cell). Viscoelastic properties of the RBCs were studied by micropipette aspiration and correlated with shape change. Ethanol-treated RBCs showed a decrease in membrane elastic modulus and an increase in membrane viscosity in the recovery phase at the early stage of shape change. MPPC-treated cells showed the same type of viscoelastic changes, but these were not observed until the formation of stage 2 echinocytes. High-resolution solid-state 13C nuclear magnetic resonance technique was applied to study membrane lipid packing in the ghost membrane by following the chemical shift of hydrocarbon chains. Both MPPC and ethanol caused the 13C-NMR chemical shift to move upfield, indicating that membrane lipids were expanded due to the intercalation of these exogenous molecules. Using data obtained from model compounds, we convert values of chemical shift into a lipid packing parameter, i.e., number of gauche bonds for fatty acyl hydrocarbon chains. Approximately 10(8) interacting molecules per cell are required to induce a detectable change of lipid packing by both MPPC and ethanol. The results indicate that homolysis occurs at a smaller surface area for MPPC- than ethanol-treated RBCs. Our findings suggest that progressive changes in the molecular packing in the membrane lead eventually to hemolysis, but the mode responsible for shape transformation varies with these amphipaths.     

Measurement of 2-deoxyglucose and 2-deoxyglucose 6-phosphate in tissues

The enzymatic methods previously described for 2-deoxyglucose (DG) and 2-deoxyglucose 6-phosphate have been refined and adapted to measurements of brain samples ranging from 50 mg wet weight to less than a microgram dry weight. Procedures for preparing such samples for assay are described. Analytical properties of the enzymes employed are given together with means for overcoming their possible short comings. Emphasis is placed on information useful for employing DG to assess rapid changes in glucose metabolism.     

Retardation of leaf senescence by inhibitors of RNA and protein synthesis

Effects of actinomycin-D (ACT), cycloheximide (CH), rifampicin (RIF) and chloramphenicol (CAP) on senescence of soybean leaf discs were investigated. All inhibitors tested are effective in retarding senescence of soybean leaf discs. However, CH is more effective than ACT, RIF and CAP, suggesting that activation of preexisting, latent metabolic systems present in the cytoplasm piays predominant role in the initiating of leaf senescence. However, the possibility that events taking place in the nucleus or chloroplast are essential for the initiation of leaf senescence cannot be excluded.