Maternal-fetal transport kinetics of copper,selenium, magnesium and iron in perfused human placental lobule: in vitro study

Transport characteristics of certain inorganic elements such as copper, magnesium, selenium and iron have been studied in maternal-fetal direction in normal pregnancies, using in vitro perfusion of isolated placental lobules. Copper, selenium, magnesium and iron salts corresponding to twice physiological concentrations were injected as a 100 l bolus, into the maternal arterial perfusate. Serial perfusate samples were collected from venous outflows for a study period of 5 min. Concentrations of various inorganic elements and their transport kinetics were determined. Transport fractions of copper, selenium, magnesium and iron averaged 0.14, 0.19, 0.06 and 0.23% of maternal load respectively. The pharmacokinetic parameters such as area under the curve, clearance, elimination constant, and time for maximum response showed some significant differences between the various elements. We speculate that copper and selenium share the same transport pathway along a concentration gradient in maternal-fetal direction, while for iron and magnesium, active transport plays a predominant role for element transfer across the human placental membrane.     

A novel tumor suppressor protein promotes keratinocyte terminal differentiation via activation of type I transglutaminase

Tazarotene-induced protein 3 (TIG3) is a recently discovered regulatory protein that is expressed in the suprabasal epidermis. In the present study, we show that TIG3 regulates keratinocyte viability and proliferation. TIG3-dependent reduction in keratinocyte viability is accompanied by a substantial increase in the number of sub-G1 cells, nuclear shrinkage, and increased formation of cornified envelope-like structures. TIG3 localizes to the membrane fraction, and TIG3-dependent differentiation is associated with increased type I transglutaminase activity. Microscopic localization and isopeptide cross-linking studies suggest that TIG3 and type I transglutaminase co-localize in membranes. Markers of apoptosis, including caspases and poly(ADP-ribose) polymerase, are not activated by TIG3, and caspase inhibitors do not stop the TIG3-dependent reduction in cell viability. Truncation of the carboxyl-terminal membrane-anchoring domain results in a complete loss of TIG3 activity. The morphology of the TIG3-positive cells and the effects on cornified envelope formation suggest that TIG3 is an activator of terminal keratinocyte differentiation. Our studies suggest that TIG3 facilitates the terminal stages in keratinocyte differentiation via activation of type I transglutaminase.     

High-resolution structure of viruses from random diffraction snapshots

The advent of the X-ray free-electron laser (XFEL) has made it possible to record diffraction snapshots of biological entities injected into the X-ray beam before the onset of radiation damage. Algorithmic means must then be used to determine the snapshot orientations and thence the three-dimensional structure of the object. Existing Bayesian approaches are limited in reconstruction resolution typically to 1/10 of the object diameter, with the computational expense increasing as the eighth power of the ratio of diameter to resolution. We present an approach capable of exploiting object symmetries to recover three-dimensional structure to high resolution, and thus reconstruct the structure of the satellite tobacco necrosis virus to atomic level. Our approach offers the highest reconstruction resolution for XFEL snapshots to date and provides a potentially powerful alternative route for analysis of data from crystalline and nano-crystalline objects.     

蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.