Biosynthesis and secretion of alpha 1 acute-phase globulin in primary cultures of rat hepatocytes

Experimental inflammation in rats led to a sevenfold increase in serum levels of alpha 1 acute-phase globulin. This increase is correlated with elevated levels of translatable mRNA for alpha 1 acute-phase globulin in the liver. Biosynthesis and secretion of alpha 1 acute-phase globulin were studied in rat hepatocyte primary cultures. An intracellular form of alpha 1 acute-phase globulin with an apparent relative molecular mass of 63 500 and a secreted form of 68 000 were found. The intracellular form of alpha 1 acute-phase globulin could be deglycosylated by endoglucosaminidase H treatment indicating that its oligosaccharide chains were of the high-mannose type. The secreted form of alpha 1 acute-phase globulin was not sensitive to endoglucosaminidase H, but was susceptible to the action of sialidase reflecting carbohydrate side-chains of the complex type. Pulse-chase experiments revealed a precursor-product relationship for the high-mannose and the complex type alpha 1 acute-phase globulin. In the hepatocyte medium newly synthesized alpha 1 acute-phase globulin was detected 30 min after the pulse. Unglycosylated alpha 1 acute-phase globulin was found in the cells as well as in the medium when the transfer of oligosaccharide chains onto the polypeptide chains was blocked by tunicamycin. Tunicamycin led to a marked delay in alpha 1 acute-phase globulin secretion.     

Effect of light intensity on ammonia assimilation in maize leaves

The effect of light on the metabolism of ammonia was studied by subjecting detached maize leaves to 150 or 1350 mol m^–2 s^–1 PAR during incubation with the leaf base in 2 mM ¹⁵NH₄Cl. After up to 60 min, leaves were extracted. Ammonia, glutamine, glycine, serine, alanine, and aspartate were separated by isothermal distillation and ion exchange chromatography. ¹⁵N enrichments were analyzed by emission spectroscopy. The uptake of ammonium chloride did not influence CO₂ assimilation (8.3 and 17.4 mol m^–1 s^–1 at 150 and 1350 mol m^–2 s^–1 PAR, respectively). Leaves kept at high light intensity contained more serine and less alanine than leaves from low light treatments. Within 1 h of incubation the enrichment of ammonia extracted from leaves rose to approximately 20% ¹⁵N. In the high light regime the amino acids contained up to 15% ¹⁵N, whereas in low light ¹⁵N enrichments were small (up to 6%). The kinetics of ¹⁵N incorporation indicated that NH₃ was firstly assimilated into glutamine and then into glutamate. After 15 min ¹⁵N was also found in glycine, serine and alanine. At high light intensity nearly half of the ¹⁵N was incorporated in glycine. On the other hand, at low light intensity alanine was the predominant ¹⁵N sink. It is concluded that light influences ammonia assimilation at the glutamine synthetase reaction.     

Thermoregulatory physiology of the carpenter bee,Xylocopa varipuncta

Summary The carpenter beesXylocopa varipuncta maintain thoracic temperatures of 33.0°C to 46.5°C during continuous free flight from 12°C to 40°C. Since the thoracic temperature excess is not constant (decreasing from 24°C at low air temperatures to 6°C at high) the bees are thermoregulating. We document physiological transfer of relatively large amounts of heat to the abdomen and to the head during pre-flight warm-up and during artificial thoracic heating. Most of the temperature increase of the head is due to passive conduction, while that of the abdomen is due to active physiological heat transfer despite a series of convolutions of the aorta in the petiole that anatomically conform to a counter-current heat exchanger. Although the thermoregulatory mechanisms during flight are far from clarified, our data suggest that thermoregulation involves a strong reliance on active convective cooling through increased flight speed.     

Different oligosaccharide processing of the membrane-integrated and the secretory form of gp 80 in rat liver.

Rat liver synthesizes a glycoprotein with Mr of 80.000 (gp 80) which is partly inserted into the plasma membrane and partly secreted into the serum. The membrane-integrated and the secretory form of this glycoprotein have an identical peptide pattern, but different N-linked glycans. Whereas gp 80 from the serum is glycosylated with complex-type oligosaccharides, gp 80 from the plasma membrane has high mannose glycans. Phase separation with Triton X-114 showed that membrane-integrated gp 80 contains hydrophobic portions, whereas secretory gp 80 has hydrophilic properties. Intracellular transport and oligosaccharide processing of gp 80 were studied in vivo in the endoplasmic reticulum, the Golgi apparatus and plasma membranes of rat liver and in serum using pulse-chase labeling with L-[35S]methionine and immunoprecipitation. Peak labeling of gp 80 was reached in the endoplasmic reticulum 10 min after the pulse, in the Golgi apparatus 20 min later, and in the plasma membrane after 2 h; in the serum the specific radioactivity was steadily increasing during the experiment. Gp 80 of the endoplasmic reticulum was completely sensitive to endo-beta-N-glucosaminidase H (endo H), but simultaneously occurred in the Golgi apparatus in an endo H-sensitive and endo H-resistant form. The endo H-sensitive form was transported to the plasma membrane, the endo H-resistant species secreted into the serum. Conversion from the endo H-sensitive to the endo H-resistant form was completed within 10 min after transfer of gp 80 to the Golgi apparatus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Different effects of the glucosidase inhibitors 1-deoxynojirimycin, N-methyl-1-deoxynojirimycin and castanospermine on the glycosylation of rat alpha 1-proteinase inhibitor and alpha 1-acid glycoprotein.

The glucosidase inhibitors 1-deoxynojirimycin, N-methyl-1-deoxynojirimycin and castanospermine were used to inhibit oligosaccharide processing in primary cultures of rat hepatocytes. Their effect on the glycosylation of alpha 1-proteinase inhibitor (alpha 1PI) and alpha 1-acid glycoprotein (alpha 1AGP) was studied. Of the three glucosidase inhibitors examined, 1-deoxynojirimycin inhibited not only oligosaccharide trimming but also glycosylation de novo of newly synthesized proteins, resulting in the formation of alpha 1PI with two and three (normally carrying three) and alpha 1AGP with two to five (normally carrying six) oligosaccharide side chains. In the presence of the glucosidase inhibitors, glucosylated high-mannose-type oligosaccharides accumulated. Whereas most of the endoglucosaminidase-H-sensitive oligosaccharides formed in the presence of 1-deoxynojirimycin contained only one glucose residue, N-methyl-1-deoxynojirimycin and castanospermine led mainly to the formation of oligosaccharides with three glucose residues. None of the three glucosidase inhibitors completely prevented the formation of complex-type oligosaccharides. Thus, in their presence, alpha 1PI and alpha 1AGP with a mixture of both high-mannose and complex-type oligosaccharides were secreted.     

In vivo visualization of individual neurons in arthropod ganglia facilitates intracellular neuropil recording

Summary A simple method for the in vivo visualization of dye filled cells by laser illumination is used to characterize neurons in situ in the segmentai ganglia of the locust and the crayfish (Fig. 1). Neuron visualization provides the structural information necessary for identification of cells during an ongoing physiological experiment (Figs. 2, 3). Sequential penetrations of soma and neuropil as well as simultaneous double neuropil penetrations of spiking and nonspiking cells are facilitated by the visual control afforded by neuron visualization (Figs. 4, 5, 6). Furthermore, neuron visualization allows the sampling of cellular properties at multiple, predetermined sites in the dendritic and axonal arbors of identified neurons (Fig. 7) and aids in establishing synaptic connectivity through double neuropil recordings (Fig. 8).     

Cooperative lipid activation of (Na+ + K+)-ATPase as a consequence of non-cooperative lipid-protein interactions

Lipid activation data for $\text{(Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-ATPase}$ (Ottolenghi, P. (1979) Eur. J. Biochem. 99, 113–131) have been subjected to a regression and fitting analysis based on a recent kinetic model (Sandermann, H. (1982) Eur. J. Biochem, 127, 123–128). The observed kinetic cooperativity could be generated from strictly non-cooperative binding events involving the known number of 30 boundary lipid-binding sites per ATPase monomer. Apparent lipid dissociation equilibrium constants of between 0.3 and 5 μM were obtained, enzyme activity being associated only with the fully lipid-substituted enzyme and enzyme-lipid complexes with less than six unoccupied lipid-binding sites. The enzyme appeared to operate close to a maximum of cooperativity.