Streptozotocin treatment of streptozotocin-induced islet cell adenomas in rats.

Hypoglycemic rats bearing insulin-secreting islet-cell adenomas produced by the combined action of streptozotocin and nicotinamide were treated with streptozotocin. Antitumor response was demonstrated by elevation of blood glucose, reduction in plasma and tumor IRI, and histopathologic changes in the beta-cell neoplasm. The rodent tumor model may serve as a predictive system for selection and investigation of mechanisms of action of future antitumor agents to be used in the treatment of malignant insulinoma in man.     

Salinity effects on photosynthesis in isolated mesophyll cells of cowpea leaves

Mesophyll cells from leaves of cowpea (Vigna unquiculata [L.] Walp.) plants grown under saline conditions were isolated and used for the determination of photosynthetic CO₂ fixation. Maximal CO₂ fixation rate was obtained when the osmotic potential of both cell isolation and CO₂ fixation assay media were close to leaf osmotic potential, yielding a zero turgor pressure. Hypotonic and hypertonic media decreased the rate of photosynthesis regardless of the salinity level during plant growth. No decrease in photosynthesis was obtained for NaCl concentrations up to 87 moles per cubic meter in the plant growing media and only a 30% decrease was found at 130 moles per cubic meter when the osmotic potential of cell isolation and CO₂ fixation media were optimal. The inhibition was reversible when stress was relieved. At 173 moles per cubic meter NaCl, photosynthesis was severely and irreversibly inhibited. This inhibition was attributed to toxic effects caused by high Cl⁻ and Na⁺ accumulation in the leaves. Uptake of sorbitol by intact cells was insignificant, and therefore not associated with cell volume changes. The light response curve of cells from low salinity grown plants was similar to the controls. Cells from plants grown at 173 moles per cubic meter NaCl were light saturated at a lower radiant flux density than were cells from lower salinity levels.     

Expression of a Clostridium thermocellum endoglucanase gene in Lactobacillus plantarum

Recombinant plasmid pM25 containing the celE gene of Clostridium thermocellum, which codes for an enzymatically active endoglucanase, was transformed into Lactobacillus plantarum by electroporation. Strains harboring pM25 expressed thermostable endoglucanase, which was found predominantly in the culture medium. Two other plasmids, pGK12 and pSA3, were transformed into L. plantarum, and the stability of each plasmid was evaluated.     

A predicted three-dimensional structure for the human immunodeficiency virus binding domains of CD4 antigen

A predicted three-dimensional structure of the two N-terminal extracellular domains of human CD4 antigen, a cell surface glycoprotein, is reported. This region of CD4, particularly the first domain, has been identified as containing the binding region for the envelope gp120 protein of the human immunodeficiency virus. The model was predicted based on the sequence homology of each domain with the variable light chain of immunoglobulins. The framework beta-sheet regions were taken from the crystal coordinates of REI. For one region in the first domain of CD4 there was an ambiguity in the alignment with REI and two alternate models are presented. Loops connecting the framework were modelled from fragments selected from a database of main chain coordinates from all known protein structures. Residues identified as involved in binding gp120 have been located in several other studies within the first domain of CD4. Epitopes from eight monoclonal antibodies have been mapped onto residues in both domains. Competition of these antibodies with each other and with gp120 can be interpreted from the structural model.     

In vitro studies of iron bioavailability

The bioavailability of iron from foods is ultimately determined by interactions between iron and other components in the digestive milieu. Perhaps the most important factor is the concentration of Fe2+ during transit through the duodenum. During in vitro simulations of human digestion it is possible to probe the concentration of Fe2+, the rate of Fe2+ formation, and total iron concentration using ferrous chromogens. It is crucial, of course, that the chromogen not interfere with the redox reactions occurring during digestion. Accordingly, ferrozine was examined with regard to its ability to reduce complexes Fe3+, alter rates of Fe3+ production, detect Fe2+ present in the digestive mixture and differentiate the effects of chelating and reducing agents in the mobilization of iron from pinto beans. The chromogen was found to be free from apparent artefacts and to be a sensitive and reproducible probe of the state of iron in digestive mixtures.     

Chromosome numbers in callirhoe (Malvaceae)

Forty-four chromosome counts from the North American genusCallirhoe are reported, including first-recorded counts ofC. alcaeoides, C. digitata, C. bushii, C. triangulata, andC. involucrata var.tenuissima. Information concerning chromosome numbers from present and previous reports is summarized and evaluated. Observations are presented on meiosis for the genus in general, for male sterile individuals of gynodioecious species, and for selected F₁ hybrids. Pollen fertility data are recorded for the latter. Chromosomally three species groups are recognized: an exinvolucellate, diploid species group withn=14; an involucellate, tetraploid and octoploid species pair,n=28 and 56; and an involucellate, diploid and tetraploid species group withn=15 and 30. Intrageneric relationships and those within the tribe Malveae subtribe Malvinae are discussed.     

The displacement of copper by iron at the specific binding sites of ovotransferrin

We have examined the kinetics and mechanism by which iron can displace copper at the specific metal-binding sites of ovotransferrin. Fe2+ was added to Cu2+-ovotransferrin-CO3(2-) in the presence of NaHCO3 and ambient O2. The reaction has been followed by standard and stopped-flow spectrophotometry, EPR spectroscopy and analysis of chromogen-reactive Fe2+. The reaction is best described as triphasic. An initial jump in absorbance takes place in the first 2 s. In the next minute there is a further increase in absorbance and shift in the spectral maximum from 440 to 446 nm. The third phase is complex. The bulk of the spectrophotometric change, a decrease in absorbance with a shift to a maximum of 453 nm, lasts approx. 3 min. Minor spectral and EPR changes, however, take place over the next several hours. Chromogenic analysis of Fe2+ indicates that approx. 1 min is required to oxidize the Fe2+. EPR spectra reveal the formation of an Fe3+-ovotransferrin complex within the first 20 s; however, this lacks the characteristic doublet of specific Fe3+-ovotransferrin-CO3(2-). The simultaneous presence of specific Cu2+-ovotransferrin-CO3(2-) and Fe3+-ovotransferrin-CO3(2-) signals suggests a period in which the protein specifically binds both metal ions perhaps resulting from a differential reactivity of the two metal-binding sites. The addition of Cu(NO3)2 to Fe3+-ovotransferrin-CO3(2-) resulted in a complex with specific Fe3+ and non-specific Cu2+. The EPR spectrum of this complex and the final product of our displacement reaction were virtually identical. Distinct parallels in reaction of Cu2+-ovotransferrin-CO3(2-) with Fe(NH4)2(SO4)2, Fe(NO3)3 and Fe3+-nitrilotriacetic acid were observed. A reaction sequence involving the binding and oxidation of non-specific Fe2+ followed by Cu2+ displacement by Fe3+ at the specific sites and binding of non-specific Cu2+ is suggested.     

Active and passive immunization of mice against larval Dirofilaria immitis

The objective of this study was to determine if Dirofilaria immitis larvae would survive in diffusion chambers implanted in dogs and mice and secondly to determine if mice could be immunized against infection with D. immitis. Dirofilaria immitis third-stage larvae (L3) survived and grew in diffusion chambers implanted in dogs and mice for at least 3 wk. BALB/c mice, which were repeatedly infected with live L3, showed resistance to challenge infections. Dead L3, with or without adjuvants elicited no protective immunity. A correlation was found between the degree of immune protection seen in mice and antibody levels to soluble larval antigen but not to antibody levels to surface antigens. A monoclonal antibody was prepared that reacted with the surface of D. immitis and Onchocerca lienalis L3, but not to the surfaces of other stages and species of various filarial worms. When this antibody was administered to mice prior to challenge no significant reduction in larval survival was observed.