The effect of tumour progression on lymphocyte responses to lectins,measured by fluorescence polarization techniques

The process of fluorochromasia involves the hydrolysis by cells of fluorescein diacetate resulting in an intracellular accumulation of fluorescein. The polarization of the fluorescence of the fluorescein appears to depend on the intracellular fluorescein concentration, the distribution of fluorescein within the cell and the viscosity of the cell cytoplasm.The parameters of fluorochromasia were studied with thymocytes from normal BALB/c mice and from mice bearing an intraperitoneal NK/LY/R lymphoma. During the course of tumour proliferation, the response toT-cell mitogens increased whereas the response to other lectins,e.g. wheat germ agglutinin, decreased or remained unaltered. These changes were consistent with the corresponding increase in immunocompetent cells within the thymus, observed by microelectrophoresis. Thus this sensitive technique provides a useful quantitative assessment of the lectin-lymphoid cell interaction.     

Molecular phylogeny and novel host associations of avian chewing lice (Insecta: Phthiraptera) from South Africa

Compared with Europe and the Americas, the ectoparasites of African birds are poorly understood, despite the avian fauna being relatively well known. Notably, previous studies documenting the host associations and genetic diversity of parasitic chewing lice of southern African birds have been limited in geographic and taxonomic scope. Recent field expeditions exploring the avian diversity in South Africa facilitated an opportunity to obtain louse specimens from a taxonomically diverse host assemblage. This study is the first to investigate avian louse host associations and diversity across a large portion of South Africa encompassing several distinct habitat types, while incorporating molecular genetic data (from portions of the mitochondrial COI and nuclear EF‐1α genes) for ectoparasite phylogenetic analyses. From 1105 South African bird individuals and 170 species examined for lice, a total of 105 new louse–host associations were observed. Morphological and genetic examination of lice with these new host associations reveals a maximum of 66 louse species new to science. Results of this study support the observation that examining museum specimens is a useful way to investigate louse diversity and host associations.     

Arabinose 5-phosphate covalently inhibits transaldolase

Arabinose 5-phosphate (A5P) is the aldopentose version of the ketohexose fructose 6-phosphate (F6P), having identical stereochemistry but lacking atoms corresponding to the 1-carbon and 1-hydroxyl. Despite structural similarity and conservation of the reactive portion of F6P, F6P acts as a substrate whereas A5P is reported to be an inhibitor of transaldolase. To address the lack of A5P reactivity we determined a crystal structure of the Francisella tularensis transaldolase in complex with A5P. This structure reveals that like F6P, A5P forms a covalent Schiff base with active site Lys135. Unlike F6P, A5P binding fails to displace an ordered active site water molecule. Retaining this water necessitates conformational changes at the A5P-protein linkage that possibly hinder reactivity. The findings presented here show the basis of A5P inhibition and suggest an unusual mechanism of competitive, reversible-covalent transaldolase regulation.     

The purification and characterization of bovine enterokinase from membrane fragments in the duodenal mucosal fluid

Bovine enterokinase has been purified from the mucosal fluid adhering to the intestinal wall. Enterokinase is predominantly present as membrane fragments which must be treated with Triton X-100 to release the enzyme. The purification resulted in a higher yield of enzyme in fewer steps and in less time than when mucosal cells were used. The properties of the enzyme in the fluid are identical with those found previously with the mucosal cell preparation (Liepnieks, J. J., and Light, A. (1979) J. Biol. Chem. 254, 1677-1683), but differ in the size of the subunits and in amino acid composition from the enzyme purified from intestinal contents (Anderson, L. E. Walsh, K. A., and Neurath, H. (1977) Biochemistry 16, 3354-3360). It is highly unlikely that the existence of isoenzymes could explain these differences. It is more likely that the enzyme isolated from the intestinal contents represents an extensively degraded form with retention of enzymatic activity.