The role of variant surface antigens on malaria-infected red blood cells.

It has been proposed that the primary role of variant antigens appearing on the surface of red blood cells infected with malaria parasites is to mediate cytoadherence, and that the antigenic variation they display is an adaptation to avoid immune attack. Here, Allan Saul proposes that their role is the opposite: that their primary purpose is to generate an immune response, which regulates their growth and thereby establishes a chronic infection, and that the role of cytoadherence is to ensure that parasites failing to express this flag to the immune system are destroyed by the spleen.     

Vitamin E Induces Phosphatidylserine Externalization and Red Cell Adhesion to Endothelial Cells

Red blood cell (RBC) adhesion to vessel wall endothelium is a potent catalyst of vascular occlusion and occurs in oxidative stress states such as hemoglobinopathies and cardiovascular conditions. These are often treated with vitamin E (VitE), a “classic” antioxidant. In this study, we examined the effects of VitE on RBC adhesion to vascular endothelial cells (EC), and on translocation of phosphatidylserine (PS) to RBC surface, known as a potent mediator of RBC/EC adhesion, facilitating thrombus formation. Treatment of RBC with VitE strongly induces (up to sevenfold) PS externalization and enhances (up to 20-fold) their adherence to EC. The VitE hydrophilic analogue—Trolox—does not incorporate into cell membranes. Trolox did not exhibit any of these effects, implying that the VitE effect is due to its known ability to incorporate into cell membranes. The membrane-incorporated VitE significantly reduced the level of reactive oxygen species in H₂O₂-treated RBC, demonstrating that VitE elevates RBC/EC adhesion despite acting as an anti-oxidant. This study demonstrates for the first time that contrary to the common view of VitE as a beneficial supplement, VitE may introduce a circulatory risk by inducing flow-disturbing RBC adherence to blood vessel wall and the pro-thrombotic PS exposure.     

Protease inhibitor controls prophenoloxidase activation in Manduca sexta

Prophenoloxidase from the hemolymph of tobacco hornworm Manduca sexta can be activated by a specific activating enzyme found in the cuticle. Inhibition studies with benzamidine, diisopropyl phosphofluoridate and p-nitrophenyl-p'-guanidinobenzoate indicate that the activating enzyme is a trypsin-like serine protease. An endogenous protease inhibitor, isolated from the hemolymph of Manduca larvae, inhibits the prophenoloxidase activation mediated by this enzyme. These results indicate that the probable physiological role of endogenous protease inhibitor is to control the undesired activation of prophenoloxidase in the hemolymph.     

Hodulcin: selective sweetness-reducing principle from Hovenia dulcis leaves

An aqueous extract of Hovenia dulcis leaves selectively reducedsweetness perception in humans. The taste-active principle,‘hodulcin’, was partially purified and comparedchromatographically with similarly prepared samples of the selective,sweetness-reducing compounds, gymnemic acids and ziziphins.Hodulcin appears to be a triterpene saponin glycoside, as arethe gymnemic acids and ziziphins. Nuclear magnetic resonance(NMR) spectra indicated an hodulcin aglycone structure differentfrom the gymnemic acids aglycone, and similar to, but not thesame as the ziziphins aglycone. Future comparative studies ofthe actions of hodulcin, gymnemic acids and ziziphins couldelucidate physiological mechanisms for the transduction andidentification of sweet stimuli and aid the development of newapproaches to the sweetening of foods.     

The 5' terminal capping of heterogeneous nuclear RNA at different embryonic stages of the sea urchin.

5' Terminal cap structures of hnRNA have been characterized and the extent of capping determined as a function of embryonic development. Sea urchin embryo hnRNA contains only the type-1 cap, m7GpppNmpNp, with the type-2 cap, which has a 2'-0-methylated subpenultimate nucleotide, being associated only with stable small nuclear RNAs. These cap 2-containing RNAs are synthesized at a rate of approximately 70 molecules min-1 nucleus-1 compared to approximately 1000 molecules for hnRNA cap 1. Approximately 70% of nuclear cap 1 is associated with greater than 15S RNA in denaturing solvent, but under non-denaturing conditions the percentage is much higher. Cap 1 in low and high molecular weight nuclear RNA have the same kinetics of methyl labeling. Thus all cap 1 structures may belong to a single class either covalent or H-bonded to high molecular weight RNA. hnRNA greater than 15S is 35% capped; however, adding caps in less than 15S RNA gives an estimate of 50% capping for total hnRNA. In development from early blastula to late gastrula, there is little if any change in the extent of capping of hnRNA. These results coupled with others indicate that the fraction of hnRNA molecules serving as precursor to mRNA does not change quantitatively during embryonic development.