Amiloride fluxes across erythrocyte membranes

Amiloride is known to inhibit both the influx of Na+ and the activation of mitogenesis in many cultured cell lines. This paper describes experiments in which the permeability coefficient of amiloride was determined from measurements of tracer fluxes across human erythrocytes and resealed ghosts. From an analysis of these fluxes, a permeability coefficient of 10(-7) cm/s for the uncharged form of amiloride was deduced. Based upon this measured permeability value, we present calculations of intracellular accumulation times of amiloride in cells of differing surface-to-volume ratio.     

Murine Ia-associated invariant chain's processing to complex oligosaccharide forms and its dissociation from the I-Ak complex

The processing of murine invariant chain (Ii) to a cell surface form bearing complex N-linked oligosaccharides has been demonstrated in the B cell lymphoma, AKTB-1b. In addition, the rate of processing of pulse-labeled Ii has been determined relative to its rate of dissociation from the alpha/beta complex of I-Ak. Ii, alpha-, and beta-chains were immunoprecipitated with anti-I-Ak or anti-Ii monoclonal antibodies. The heretofore uncharacterized complex oligosaccharide form of Ii (Ii-c) was identified in gel-purified immunoprecipitates by peptide mapping with reverse-phase HPLC. Ii-c is resistant to deglycosylation by Endo H, which is specific for high-mannose N-linkages, but can be digested with Endo F, a glycosidase capable of cleaving both complex and high-mannose N-linked oligosaccharides. Immunoprecipitation of surface iodinated cells indicates that Ii-c is expressed on the plasma membrane. Pulse-chase metabolic labeling data show that the processing of Ii to Ii-c occurs with a t1/2 of about 120 min. In contrast, the processing of both alpha- and beta-chains of I-Ak to complex forms occurs with a t1/2 of 15 to 20 min. Our data show that Ii-hm begins to dissociate rapidly from the I-Ak complex after 100 to 120 min of chase. Only a small amount (less than 5% on a per mole basis) of Ii-c was found associated with the I-Ak complexes after 300 min of continuous metabolic labeling. These results are consistent with Ii serving as a carrier for Ia antigens as they are transported to the cell surface. In addition, they suggest that the processing of Ii to Ii-c, or a late processing event of the alpha- and beta-chains, such as their sialylation, may be a possible mechanism for inducing the dissociation of Ii from the I-Ak complex.     

Effect of a Cloned DNA Fragment from Streptomyces chrysomallusNo. 2 on the Metabolism of Certain Streptomyces Strains

The effects on a cloned DNA fragment carrying an actinomycin resistance determinant on physiological processes in strains of streptomycetes with various potencies in producing this antibiotic, their inactive mutants, and the model strain ofStreptomyces lividans66 were studied. This fragment was shown to modulate bacterial resistance to actinomycin and biosynthesis of antibiotics.     

Construction of a human cytochrome c gene and its functional expression in Saccharomyces cerevisiae

The nucleotide sequences of a partial cDNA and three pseudogenes of human cytochrome c were determined. The complete nucleotide sequences which encode human cytochrome c were constructed on the basis of one of the pseudogenes by in vitro mutagenesis. The constructed human cytochrome c was functionally expressed in Saccharomyces cerevisiae. The recombinant human cytochrome c was purified and characterized.     

Influence of intertree distance on foraging behaviour of Rhagoletis pomonella in the field

Abstract. 1. We tested a prediction from contemporary foraging theory that animals should decrease their allocation of energy to the searching of individual patches when interpatch travel costs decrease.
2. We used individual Rhagoletis pomonella Walsh (Diptera: Tephritidae) females foraging for oviposition sites (= Crataegus fruit) in a host tree which was surrounded by four other trees at varying distances.
3. We found that flies generally invested less search, measured as time spent searching a tree or number of leaves visited on a tree, when neighbouring trees were nearby than when farther away.
4. Under our test conditions, flies appeared to have difficulty locating neighbouring trees at a distance of more than 1.6 m.
5. Our study calls into question the interpretation of search effort by insects within resource patches in the absence of information on interpatch distances.     

Interaction between the Msh2 and Msh6 Nucleotide-binding Sites in the Saccharomyces cerevisiae Msh2-Msh6 Complex

Indirect evidence has suggested that the Msh2-Msh6 mispair-binding complex undergoes conformational changes upon binding of ATP and mispairs, resulting in the formation of Msh2-Msh6 sliding clamps and licensing the formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes. Here, we have studied eight mutant Msh2-Msh6 complexes with defective responses to nucleotide binding and/or mispair binding and used them to study the conformational changes required for sliding clamp formation and ternary complex assembly. ATP binding to the Msh6 nucleotide-binding site results in a conformational change that allows binding of ATP to the Msh2 nucleotide-binding site, although ATP binding to the two nucleotide-binding sites appears to be uncoupled in some mutant complexes. The formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes requires ATP binding to only the Msh6 nucleotide-binding site, whereas the formation of Msh2-Msh6 sliding clamps requires ATP binding to both the Msh2 and Msh6 nucleotide-binding sites. In addition, the properties of the different mutant complexes suggest that distinct conformational states mediated by communication between the Msh2 and Msh6 nucleotide-binding sites are required for the formation of ternary complexes and sliding clamps.