Rapid switching to multiple antigenic and adhesive phenotypes in malaria.

Adhesion of parasitized erythrocytes to post-capillary venular endothelium or uninfected red cells is strongly implicated in the pathogenesis of severe Plasmodium falciparum malaria. Neoantigens at the infected red-cell surface adhere to a variety of host receptors, demonstrate serological diversity in field isolates and may also be a target of the host-protective immune response. Here we use sequential cloning of P. falciparum by micromanipulation to investigate the ability of a parasite to switch antigenic and cytoadherence phenotypes. Our data show that antigens at the parasitized cell surface undergo clonal variation in vitro in the absence of immune pressure at the rate of 2% per generation with concomitant modulations of the adhesive phenotype. A clone has the potential to switch at high frequency to a variety of antigenic and adhesive phenotypes, including a new type of cytoadherence behaviour, 'auto-agglutination' of infected erythrocytes. This rapid appearance of antigenic and functional heterogeneity has important implications for pathogenesis and acquired immunity.     

甲烷氧化偶联制C2烃La2O3基催化剂的研究

本文的实验结果表明,具有开放型本征构型的La_2O_3对甲烷氧化偶联反应有相当好的活性和选择性,在750℃、原料气空速6.O×10~4ml.g~(-1).h~(-1),CH_4:O_2:N_2=3.7:l.0:9.0(V/V)的反应条件下,氧接近全部转化,甲烷转化率达25.4％,C_2烃选择性为43.6％,添加碱土金属(Ca、Sr、Ba)氧化物或碳酸盐能显著地改善催化剂的性能,在上述反应条件下,60mol％Ba-La_2O_3催化剂的C_2烃选择性达到58％。     

杂多酸荷移跃迁盐系列研究（Ⅰ）—Keggin结构杂多酸的荷移跃迁盐的合成和表征

利用电解结晶法合成了Ｋｅｇｇｉｎ结构杂多酸荷移跃迁盐（ＢＥＤＴ－ＴＴＦ）８［ＰＭｏ３ＮｂＷ８Ｏ４０］．Ｘ－射线衍射测定为单斜晶系．晶胞参数ａ＝１４．２０（０）×１０（－８）ｃｍ；ｂ＝４３．３９（０）×１０（－８）ｃｍ；ｃ＝１３．５５（６）×１０（－８）ｃｍ；β＝９１°；Ｖ＝８．３５３×１０（－２１）ｃｍ３．该化合物具半导体性质。σｒ．ｔ＝３．７×１０（－２）Ｓｃｍ（－１）．ＥＡ＝１６０ｍｅＶ．变温磁化率测定表明其为Ｓｐｉｎ－Ｐｅｉｅｒｌｓ体系．     

木槿（Hibiscus syriacusL.）耐盐变异体的选择

木槿愈伤组织耐盐细胞系是在含ＮａＣｌ的培养基上通过屡代选择产生的，在无盐培养其中进行几代继代培养后的愈伤组织，由其分化的芽以及脱分化增殖的愈伤组织均表现了耐盐性，木槿耐盐细胞由于对ＮａＣｌ的反应比未经选择的细胞积累了更多的Ｎ＾＋，Ｋ＾＋，而且细胞体积较小。     

Pectinoacetals A-C: novel sterol hemiacetals from the gorgonianCtenocella pectinata

Three polyhydroxylated sterol hemiacetals, pectinoacetals A-C (1–3) have been isolated as their acetyl derivatives (4–6) from the acetic anhydride treated organic extract of the Indo-Pacific gorgonianCtenocella pectinata. These natural products were found to undergo very rapid epimerization at the C-18 chiral center and thus exist only as an equilibrium mixture of two diastereomers. The structure assignments are based on spectral studies and chemical modifications of the natural products.     

Sexual isolation betweenDrosophila melanogaster females andD. simulans males. Male mating propensities versus success in hybridization

Genetic variation has been found in males of aD. simulans population for their eagerness to hybridize withD. melanogaster females. In a search for traits involved in this hybridization, males ofD. simulans were tested for mating speed and sexual vigour. Between-male differences were detected in both sexual traits, but no relationship was noticed between them, nor with the frequency of hybridization. Thus male mating propensities appear to be unrelated to the breakdown of sexual isolation between these sibling species.     

The effect of scale changes on repetitive patterns: Influence of 6-aminonicotinamide on feather germ number

There are many examples of patterned developing systems which are size invariant: if the total size of the system is reduced, then the pattern responds by changing its scale in such a way that the number of pattern elements remains constant. This phenomenon is one of the bases which underaly the formulation of the concept of positional information, one of the great unifying ideas in developmental biology. However, there are less common examples of patterns which are size dependent. In these, alterations of overall size lead to a reduction in pattern elements. Such size-dependent patterns are therefore of theoretical interest. Here we describe how the number of feather germs along the wing bud of the developing chick embryo responds to shortening of the limb, and consider the implications of these observations.     

Photoreceptor damage following exposure to excess riboflavin

Flavins generate oxidants during metabolism and when exposed to light. Here we report that the photoreceptor layer of retinas from black-eyed rats is reduced in size by a dietary regime containing excess riboflavin. The effect of excess riboflavin was dose-dependent and was manifested by a decrease in photoreceptor length. This decrease was due in part to a reduction in the thickness of the outer nuclear layer, a structure formed from stacked photoreceptor nuclei. These changes were accompanied by an increase in photoreceptor outer segment autofluorescence following illumination at 328 nm, a wavelength that corresponds to the excitation maxima of oxidized lipopigments of the retinal pigment epithelium.     

Extraordinary levels of cadmium and zinc in a marine sponge,Tedania charcoti Topsent: inorganic chemical defense agents

The Antarctic marine spongeTedania charcoti has been shown to contain extraordinarily high natural concentrations of cadmium and zinc, which have in turn been correlated to the ability of the crude ethanol extract to modulate protein phosphorylation in chicken forebrain and to inhibit the growth of several test bacteria.     

Membrane transport of Na and K and cell dehydration in sickle erythrocytes

The cellular concentration of Hb S plays a central role in the kinetic of Hb S polymerization and cell sickling. Blood of patients with homozygous sickle cell (SS) anemia contains a variable fraction of cells which are markedly dehydrated and have increased Hb S concentration. Since a decrease in cellular Hb S concentration reduces Hb S polymerization and sickling, the study of the processes leading to sickle cell dehydration has important pathophysiological and therapeutic implications. Sickle cell dehydration is due to cellular loss of K and Cl. K loss in sickle cells can take place via either the Ca²⁺-activated K⁺ channel, or the K?Cl cotransport, or the combined effect of oxidative damage and deformation of the red cell membrane. Inhibitors of K transport through these pathways could be used to prevent dehydration of sickle cells in vivo, provided that they can be administered safely.