Erythrocytes infected with trophozoites and schizonts ofthe human malaria parasite Plasmodium falciparum develop surface protrusions (knobs) (1) by which the infected erythrocytes (IRBCs)t adhere specifically to venular endothelium in vivo (2, 3) and to human endothelial cells (4) and some lines of melanoma cells (5) in vitro. Cytoadherence between IRBCs and venular endothelium has a critical role in the pathogenesis of falciparum malaria, since it permits the mature parasites to evade spleen-dependent immune mechanisms (6) and since the sequestered parasites may occlude blood flow, as seen in cerebral malaria (7). Antibody in immune serum reacts with a strain-specific parasite-determined antigen on IRBCs and inhibits cytoadherence in vitro (8) and in vivo (9). The inhibition of cytoadherence by antibody may protect the host from the clinical consequences of falciparum malaria.Both cytoadherence and the IRBC surface antigen were shown to be destroyed by incubating IRBCs with proteases (9, 10), suggesting that the two properties are determined by proteins on the IRBC surface. In addition, the cytoadherence phenotype ofP.falciparum parasites and the expression ofthe IRBC surface antigen were modulated together by the spleen in a monkey model of falciparum malaria (9, 10), suggesting that the two properties are linked and perhaps determined by the same protein. A family ofpotential cytoadherence proteins was identified in studies with IRBCs from Aotus monkeys (11) . The members ofthe protein family differed in antigenicity and molecular size among strains ofP.falciparum, but had in common several biochemical properties, including their accessibility to surface radioiodination, detergent solubility, and cleavage by the same concentration of trypsin that inhibited cytoadherence (11) .
UDP glucuronosyltransferases (UGTs) comprise a multigene family of drug-metabolizing enzymes. The subfamily of UGTs that conjugate bilirubin and phenolic compounds with glucuronic acid has been termed UGT1A1. In man, UGTIAI isoforms are encoded by a single gene, UGT1A1. Protein isoforms encoded by UGT1A1 originate by alternative splicing. In the present study, we used the cDNA of UGT1A1*4, a bilirubin-conjugating isoform, to localize the UGT1A1 locus in the human genome. The UGT1A1 gene was assigned by in situ hybridization to chromosome region 2q37.
Conventional fixation for thin-section microscopy is insufficient to preserve many elements of cells and tissues. Actin filaments, for example, are destroyed during post-fixation in OsO4. In our search for a better fixative, we chose pellets of pure actin filaments as a very sensitive model system. In the present study, the potential of amines for improving aldehyde fixation was explored, and the results were compared to those obtained with the use of tannic acid. Aldehyde and amine were used together as an initial fixative, followed by aldehyde alone with postfixation in 1% OsO4 in buffer at 4 degrees C for 15 min, uranyl acetate en bloc stain, acetone dehydration, and embedding in Epox 812. Some primary monoamines improved the preservation of filaments; filaments were not broken beyond recognition by OsO4, as occurs when glutaraldehyde alone is used. Excellent preservation was seen when certain primary diamines were used. The quality of this fixation was superior to that obtained with tannic acid and was without the large increase in filament diameter that is seen with concentrations of tannic acid sufficient to protect filaments against osmium damage. The effects on filaments of the amines lysine, putrescine, ammonium, and arginine have been documented in detail, as we systematically varied all the major parameters normally considered in formulating fixation protocols.
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