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).     

Similarity of activation of yeast phosphofructokinase by AMP and fructose-2,6-bisphosphate

Phosphofructokinase from yeast is effectively activated by AMP and fructose-2,6-bisphosphate by increasing the affinity of the enzyme to fructose-6-phosphate and the maximum activity toward this substrate. The enzyme is activated by AMP and fructose-2, 6-bisphosphate both at high and at low concentrations of ATP. The half maximum stimulation concentrations of AMP and fructose-2, 6-bisphosphate are about 200 microM and 2 microM, respectively. At saturating concentrations of AMP and fructose-2, 6-bisphosphate similar maximum activities were observed in the dependence of enzyme activity on the concentrations of fructose-6-phosphate. The fructose-6-phosphate affinity is more enhanced by fructose-2, 6-bisphosphate than by AMP.     

Human tissue kallikrein. I. Isolation and characterization of human pancreatic kallikrein from duodenal juice

Human pancreatic kallikrein was purified from duodenal juice by ion exchange chromatography on DEAE-Sepharose and immunoaffinity chromatography. Thus, an enzyme preparation with a specific activity (using Ac-Phe-Arg-OEt as substrate) of 1 000 U/mg protein was obtained. A specific biological activity of 1310 KE/mg protein was measured in the dog blood pressure assay and of 0.361 HMW kininogen-U/mg, corresponding to the liberation of 383 micrograms bradykinin-equivalents per mg enzyme per min from HMW kininogen in the rat uterus assay. In dodecyl sulfate gel electrophoresis one protein band corresponding to a molecular mass of 27 kDa was obtained. Using gel filtration on Ultrogel AcA-44 a molecular mass of 40 kDa was measured. The amino-acid composition was determined and isoleucine and alanine were identified as the only N-terminal amino-acid residues. On isoelectric focusing four protein bands with isoelectric points of 5.60, 5.65, 5.70 and 5.85 were separated. The bimolecular velocity constant for the inhibition by diisopropyl fluoro phosphate was determined as 10.5 l x mol-1 x min-1. The dissociation constant Ki of the human pancreatic kallikrein-aprotinin complex was calculated to be 1.5 x 10(-10)M. The kinetic constants for the kallikrein-catalysed hydrolysis of Ac-Phe-Arg-OEt and D Val-Leu-Arg-Nan were determined. Immunological studies showed a close relationship between the human pancreatic kallikrein and other human tissue kallikreins, especially with human urinary kallikrein. Detergents such as Triton X-100, Tween 20 and lysolecithin, as well as human serum albumin, activated the human pancreatic kallikrein preparation.     

A kinetic study on the enzymatic hydrolysis of fluorescein diacetate and fluorescein-di-beta-D-galactopyranoside

The kinetics of the hydrolysis of fluoresceindiacetate and fluorescein-di-beta-D-galactopyranoside were investigated by thin-layer chromatography. The time course of the concentrations of substrate, monosubstituted intermediate, and product was simulated numerically. The mathematical model takes into account the competition of substrate and intermediate and the accumulation of the intermediate at the enzyme.     

Uptake of l-Ascorbate by Intact Spinach Chloroplasts

Uptake of l-[1-¹⁴C]ascorbate by intact ascorbate-free spinach (Spinacia oleracea L. cv Vital^r) chloroplasts has been investigated using the technique of silicone oil filtering. Rates greater than 100 micromoles per milligram chlorophyll per hour (external concentration, 10 millimolar) of ascorbate transport were observed. Ascorbate uptake into the sorbitol-impermeable space (stroma) followed the Michaelis-Menten-type characteristic for substrate saturation. A K_m of 18 to 40 millimolar was determined. Transport of ascorbate across the chloroplast envelope resulted in an equilibrium of the ascorbate concentrations between stroma and medium. A pH optimum of 7.0 to 7.5 and the lack of alkalization of the medium upon ascorbate uptake suggest that only the monovalent ascorbate anion is able to cross the chloroplast envelope. The activation energy of ascorbate uptake was determined to be 65.8 kilojoules (16 kilocalories) per mole (8 to 20°C). Interference of ascorbate transport with substrates of the phosphate or dicarboxylate translocator could not be detected, but didehydroascorbate was a competitive inhibitor. Preloading of chloroplasts with didehydroascorbate resulted in an increase of V_max but did not change the K_m for ascorbate. Millimolar concentrations of the sulfhydryl reagent p-chloromercuriphenyl sulfonate inhibited ascorbate uptake. The data are interpreted in terms of ascorbate uptake into chloroplasts by the mechanism of facilitated diffusion mediated by a specific translocator.