Effects of forskolin and cholera toxin on cyclic AMP release in a neurotensin-secreting rat C-cell line

The effects of forskolin and cholera toxin on the regulation of cAMP release were studied in a neurotensin-secreting rat C-cell line. The interaction of these agents with norepinephrine, a potent neurotensin secretagogue, was also investigated. Forskolin stimulated cAMP release 10(2)-10(3) fold while it increased neurotensin release 2-3 fold. Cholera toxin caused a 10(2)-10(3) fold increase in cAMP release and had no effect on neurotensin release. We conclude that the 44-2 C-cells provide a new model for studying the regulation of the concomitant (via forskolin) or independent (via cholera toxin) secretion of cyclic AMP and/or neurotensin.     

Purification of restriction endonuclease XcyI from Xanthomonas cyanopsidis

A new Type II restriction endonuclease XcyI, purified from Xanthomonas cyanopsidis 13D5, is an isoschizomer of SmaI and XmaI that cleaves at the nucleotide sequence 5'-C decreases CCGGG-3' of double-stranded DNA. The single restriction activity present in this strain permits rapid purification of 8000 units of cleavage activity from 10 g of freshly harvested cells. The resulting XcyI preparation is free of contaminating nuclease activities that interfere with in vitro manipulation of DNA.     

Antigen of "serum sickness" type of heterophile antibodies in human sera: indentification as gangliosides with N-glycolylneuraminic acid.

Antigen of “serum-sickness” type of heterophile antibodies in pathologic human sera was purified from equine and bovine erythrocyte stroma. The chemical nature of this antigen was glycosphingolipids with N-glycolylneuraminic acid. The antigen of equine erythrocytes was identified as hematoside with N-glycolylneuraminic acid, GlNeu(α, 2–3)Gal(β, 1–4)Glc(β,1-1) ceramide and the antigen of bovine erythrocytes was N-glycolylneuraminyl-paragloboside, GlNeu (α,2–3)Gal(β,1–4)GlcNAc(β,1–3)Gal(β,1–4)Glc(β,1-1) ceramide. The results indicate that “serum-sickness” antibodies react with a common disaccharide moiety of non-reducing end of the both glycosphingolipids.     

Modification of oligosaccharide-lipid synthesis and protein glycosylation in glucose-deprived cells

Incubation of vesicular stomatitis virus-infected glucose-starved baby hamster kidney cells with [³⁵S]methionine results in the synthesis of all viral proteins. However, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tryptic peptide mapping, the G protein is abnormally glycosylated. Metabolic labeling of the oligosaccharide-lipid precursors with [³H]mannose for 15 min, followed by Chromatographic and enzymatic analysis, indicates that the radiolabeled lipid-linked oligosaccharides are devoid of glucose in contrast to the glucosylated oligosaccharide-lipids synthesized by cells grown in the presence of glucose. Also, in contrast to control cells, examination of the glycopeptide fraction reveals the presence of [³H]mannose-labeled glycopeptides which are resistant to erado-β-N-acetylglucos-aminidase H and are smaller in size than glycopeptides from mature vesicular stomatitis virus. In order to observe these effects, a minimum time of 5 h of glucose deprivation is necessary and the addition of 55 μm glucose or mannose to the medium reverses these effects. These results indicate that vesicular stomatitis virus-infected BHK cells deprived of glucose are unable to glucosylate the oligosaccharide-lipid intermediates and, consequently, are unable to glycosylate the G protein normally.     

Rat and human embryo and post-natal sera contain a potent endogenous competitor of estrogen-rat alpha-fetoprotein interactions

A highly active inhibitor of the binding of estrone and estradiol-17β to rat alpha-fetoprotein is demonstrated for the first time in embryo, immature and adult rat sera as well as in fetal and adult human sera. The competitive character and the narrow specificity of this inhibition effect is shown. The major compound responsible for this activity is isolated by successive column Sephadex LH₂₀ and thin layer chromatography : it is characterized as a nonpolar, nonphenolic, dialysable and thermostable substance, unreactive towards anti-estrone and anti-estradiol-17β anti-bodies. The possible biological role of an endogenous non-estrogen ligand of rodent fetoproteins is discussed.     

ENHANCED TRANSPORT OF INORGANIC CARBON INTO ALGAL CELLS AND ITS IMPLICATIONS FOR THE BIOLOGICAL FIXATION OF CARBON1,2

Kinetics of uptake of inorganic carbon by the freshwater green alga Chlamydomonas reinhardtii Dang. suggest that rates of fixation may be enhanced at low tensions of CO₂ by transport of bicarbonate from the cell surface to the chloroplast. Results are evaluated in the context of models that treat diffusion and reaction of dissolved inorganic carbon across a 3 dimensional finite boundary layer, and they are consistent with the claim that CO₂ alone is the substrate used during carbon fixation. An alternative hypothesis, which presumes that both CO₂ and bicarbonate are used as substrates, yields predictions which are inconsistent with the data. Instead, bicarbonate seems to act only as a vehicle for the transport of inorganic carbon into the cell, thereby adding its flux to that of CO₂, and enhancing rates of synthesis that would otherwise be restricted by uptake of CO₂ alone.     

DIVERSITY IN THE MECHANISM OF CARBON DIOXIDE FIXATION IN DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

The mechanism of photosynthetic carbon dioxide fixation in the green flagellate Dunaliella tertiolecta Butcher varies during growth in batch culture. Evidence for this change comes from three sources: i) algae from the stationary phase incorporated a greater proportion of the fixed carbon into amino arids and protein than did cells from the mid-exponential phase; ii) the activity of phosphoenolpyruvate carboxylase relative to that of ribulose-1, 5-di-phosphate carboxylase increased with age in batch culture; and, iii) cells from the stationary phase appeared to utilize the bicarbonate ion as the substrate for photosynthesis, whereas those from mid-exponential phase appeared to utilize fire carbon dioxide. These data suggest that a change of photosynthetic mechanism can occur within a single species of alga, depending on its physiological state.     

Changes in liver nuclear protein metabolism after a single dose of urethane to suckling mice

Treatment of 8-9-day-old C57BL/A mice with a single carcinogenic dose of urethane, at 1.2 mg/g body wt., resulted in an immediate decrease in liver DNA synthesis reaching a maximum at about 16-18 h after injection, the rate of synthesis returning to normal after 48 h. When the nuclear proteins were radiolabelled, the non-histone protein (NHP) fraction showed a significant decrease in specific activity 8-18 h after injection of urethane and slight increase in specific activity after 24 h. Histone and residual proteins did not show any significant change. The liver NHP were analysed by isoelectric focusing (IEF) and sodium dodecyl sulphate (SDS) electrophoresis in polyacrylamide gels. The latter technique failed to show any distinctive differences but IEF results indicated some quantitative and qualitative changes in protein content and synthesis were induced by the urethane treatment. The most noticeable change in the stained gels was an increase in a protein component having a pI of 7.35 and the appearance of new bands at pI's of 7.85 and 5.55 in the 18 h treated livers. However, the [3H]tryptophan labelling pattern indicated that this was not due to an increased synthesis of these components. 24 h after urethane there appeared to be an increased rate of synthesis of some of the major components of the mixture, particularly at the pI 5.65 region. Histone and residual protein fractions were also analysed by electrophoresis and showed no difference between treated and control livers.