Rapid In Vitro Prescreen for Chelators as Potential Trypanocides Based on Growth of Crithidia fasciculata1

A rapid in vitro prescreen for Fe-binding chelators has been developed with growth of Crithidia fasciculata and the sparing of its heme requirement in a defined medium as a test system. The prescreen functions as an index of chelator-mediated Fe transport and as an index of growth inhibition, presumably by the interference with Fe and/or heme metabolism at intracellular chelatable sites. Of 161 chelators examined, 84 were active heme-sparers; 32 of these inhibited growth at low chelator concentrations. Twenty-eight other chelators inhibited growth and another 49 were inactive. Such chelating activity directed at Fe and heme targets in hemoflagellates may provide leads for chemotherapy.     

Biochemical characterization of activation-associated bovine class I major histocompatibility complex antigens

Summary. Utilizing a 'sandwich' ELISA assay we have been able to demonstrate that mAb W6/32, B1G6 and IL-A19 are reactive with three different monomorphic determinants on bovine class I major histocompatibility complex (MHC) molecules. Sequential immunoprecipitations performed with the mAb revealed that class I molecules on PBM comprise a single population with respect to reactivity with the mAb in that the β2m-associated proteins bear all three epitopes. By contrast, TCGF-driven lymphoblasts and cells transformed by Theileria parva (Tp) additionally express molecules of Mr 45000 bound to β2m which are recognized by mAb B1G6 and IL-A19 but not by W6/32. These two subclasses of molecules were further distinguished on the basis that, when tunicamycin was added to cultures in the preparation of cells for analysis, mAb W6/32 precipitated class I heavy chains of Mr 39000 while the extra molecules detected only by mAb B1G6 and IL-A19 were of Mr 37000 and 39000. On thymocytes, the mAb W6/32-non-reactive class I molecules are present in low amounts and are expressed by cells in the medulla area, unlike BoT1 (analogous to human CD1) molecules which are expressed by the cortical cells. Our studies also revealed that the supposed β2m-specific mAb B1G6 does not recognize the β2m-associated molecules (BoT1) precipitated by mAb TH97A and thus the specificity of mAb B1G6 in cattle is for an epitope on bovine β2m which is strongly influenced by the nature of the heavy chain with which the β2m is associated.     

Late Paleozoic stromatolites: new insights from the Lower Permian of Kansas

Carboniferous to Permian marine stromatolites are widely dispersed across the Pangaean margins and embayments and are typified by the ‘Ottonosia-grade stromatolite’ (designated herein). This stromatolite type consists of a well-laminated oncoid or domical stromatoid that developed into branching, laminated columns in the upper reaches. To develop a model for the global pattern, we investigated Lower Permian stromatolites from Kansas (Howe Limestone Member, Red Eagle Limestone). Stromatoids from the Lyon County locality typify the Ottonosia-grade stromatolites. The laminae are sharp throughout the stromatoid and are defined by an increase in cornuspirid foraminfera and algal filaments. The upper zone of the stromatoid is composed of well-laminated branching and brecciated columns (‘pseudo-thrombolitic’). Coeval stromatolites from a new exposure at the Tuttle Creek Dam spillway possess a more massive mesostructure. These stromatolites are composed of a turbinate stromatoid or oncoid base and an overlying domical stromatoid, and are rimmed by smaller meandering columns. Only the basal stromatoid, oncoids, and upper columns are well laminated. In both localities, the microbial-constructing ecosystem is dominated by cornuspirids and calcifying filamentous algae (?Girvanella). The mesostructural differences of the stromatolites are due to different environments of formation. The Tuttle Creek stromatolites formed in a shallow-subtidal to intertidal open marine setting. The coeval Lyon County stromatolites formed in a semi-restricted, marginal marine environment such as a lagoon or supratidal zone. Based on this information and independent sedimentological data, we conclude that lagoonal or supratidal zones were common features in the late Paleozoic intracratonal zones of the Pangaean supercontinent and account for Ottonosia-grade stromatolites occurring in the Laurentian mid-continent, the Zechstein Basin, Japan, Brazil, and Tunisia.