Cross-sectional Area-corrected Compression Modulus of Food Gel

The linearity of the stress-strain relationship for food gel is limited to a very narrow range of the strain (usually less than 0.1 as a Cauchy measure). The reason is thought due to the change in cross-sectional area of the gel upon deformation. In this report, the cross-sectional area was approximately corrected of the compressed gel on the assumption that the gel expanded uniformly without changing its volume upon compression. In cases when the initial Young’s modulus was calculated from the thus-corrected area for some food gels, the linearity was increased for a wider range of strain.     

Different effects of sphingosine, R59022 and anionic amphiphiles on two diacylglycerol kinase isozymes purified from porcine thymus cytosol

Porcine thymus cytosol contains two immunologically distinct forms of diacylglycerol kinase (DGK) [Yamada, K. and Kanoh, H. (1988) Biochem. J. 255, 601-608]. These 2 DGK species, having apparent molecular masses of 80 and 150 kDa, were purified from the thymus cytosol. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the 150-kDa DGK gave 2 polypeptide bands of 50 and 75 kDa, whereas the 80-kDa DGK yielded a single protein band. The 80-kDa DGK was markedly activated by 10-20 microM sphingosine as well as by the known anionic activators such as phosphatidylserine and deoxycholate. In contrast, the 150-kDa DGK was fully active in the absence of the anionic activators and was strongly inhibited by sphingosine (IC50, 20 microM). The putative DGK inhibitor R59022 inhibited the 80-kDa DGK (IC50, 10 microM), but had little effect on the 150-kDa form. It is therefore clear that in the thymus cytosol there are at least 2 DGK isozymes operating under different control mechanisms.     

Cooperative conformational change and aggregation of concanavalin A in alkaline solutions

Three properties, the binding activity to Sephadex G-75, conformation, and the extent of aggregation, of concanvalin A. (con A) in alkaline pH solutions were examined with special attention to the time course and their time-independent final values. Highly cooperative conformational changes among four subunits were suggested which were coupled either with protonation in the case of demetallized con A or with metal binding in the case of metal-liganded con A. Midpoints of the conversions of the metal-liganded con A were about pH 8.8, 9.1 and 9.1 with respect to the activity, the conformational change and the aggregation, respectively. These values were about 1 pH higher than the corresponding values of demetallized con A: 7.9, 8.05 and 8.2. Each conversion took place in narrow pH ranges. The pH range for the loss of activity was found to be significantly lower than those of the other two. The aggregation was suggested not to be coupled with the conformational change. Dissociation into subunits did not take place indicating strong interactions among four subunits in the tetramer.     

Detection of tetrodotoxin by thin-layer chromatography/fast atom bombardment mass spectrometry

A new method for detection of tetrodotoxin (TTX) by thin-layer chromatography/fast atom bombardment (FAB) mass spectrometry was developed. TTX and/or related substances were separated by TLC on LHP-K high-performance precoated plates, with a solvent system of pyridine:ethyl acetate:acetic acid:water (15:5:3:4). The plates were subjected to positive FAB mass spectrometry, under scanning within a mass range from m/z 100 to 500. TTX was identified by selected ion-monitored chromatograms at m/z 320 (M + H)+ and 302 (M + H - H2O)+, along with full scan positive ion FAB mass spectrometry. The limit of detection for TTX was about 0.1 micrograms. TTX was also detected by cellulose acetate membrane electrophoresis/FAB mass spectrometry.     

Immunological characterization of sn-1,2-diacylglycerol and sn-2-monoacylglycerol kinase from pig brain

Rabbit antisera were raised against diacylglycerol kinase purified from pig brain cytosol. Upon immunoblot analysis, the antibody was specifically reactive with the kinase (Mr = 79,000-80,000). Pig brain cytosol, microsomal, and synaptosomal fractions all contained the immunoreactive Mr = 80,000 polypeptide, thus showing that the same enzyme is present in the soluble as well as membrane fractions of the brain. The antibody could precipitate only 60% of the kinase activity present in the crude cytosol. Further, the antibody exhibited very little or no cross-reactivity toward liver cytosolic enzymes obtained from different animals including pigs. Immunostaining of brain tissues demonstrated that neurons, in particular, their nuclei, were positively stained, whereas glial cells were not stained. It is likely that there exists a tissue-and/or cell-dependent immunological multiplicity of diacylglycerol kinase. The enzyme activities phosphorylating sn-1 and sn-2 monoacylglycerols were co-precipitated by the antibody, indicating their identity with diacylglycerol kinase. The enzyme activity toward sn-1 monoolein was much lower than that obtained with sn-2 monoolein. Enzymic as well as chemical analyses of acyl isomers of the reaction products showed that even tested with pure (greater than 95%) sn-1 monoolein, about 70% of the formed lysophosphatidate was of the sn-2 acyl type. The results show that diacylglycerol kinase phosphorylates almost exclusively the sn-2 acyl type of monoacyl-glycerol.     

Diacylglycerol kinase from pig brain. Purification and phospholipid dependencies

Diacylglycerol kinase (EC 2.7.1.-) was purified 1,650-fold from pig brain cytosol. The purified enzyme showed a single protein band on polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate. The molecular weight of the kinase was estimated to be 78,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A similar value (76,000) was obtained by Sephadex G-150 gel filtration. The activity of the purified enzyme was markedly enhanced by either deoxycholate or phospholipids. The extent of activation by phospholipids was in the order of phosphatidylcholine greater than lysophosphatidylcholine greater than phosphatidylethanolamine approximately equal to phosphatidylserine greater than sphingomyelin. Other phospholipids and unsaturated fatty acids were ineffective. Phosphatidylcholines from egg yolk and pig brain, and dioleoyl phosphatidylcholine were similarly effective. Saturated phosphatidylcholines with acyl chain lengths shorter than palmitate also gave a considerable activation. The activity with phosphatidylcholine was from 1.5- to 2.5-fold higher than that measured with deoxycholate. A very small amount of phosphatidylinositol or phosphatidylglycerol potently inhibited the phosphatidylcholine-dependent (but not deoxycholate-dependent) kinase activity. The inhibition by phosphatidylinositol was varied according to its molar ratio to phosphatidylcholine. As little as about 2.5 mol per cent of phosphatidylinositol resulted in 50% inhibition of the phosphatidylcholine-dependent kinase activity. The deoxycholate- and phosphatidylcholine-dependent kinase activities showed almost the same Km values for the substrates. In both cases, the apparent Km values for ATP and diacylglycerol were 300 microM and about 60 microM, respectively. The kinase required Mg2+ for its activity. When compared to deoxycholate, phosphatidylcholine was more effective at higher Mg2+ concentrations. The deoxycholate-dependent activity showed a broad pH optimum at around 8.0, whereas the phosphatidylcholine-dependent activity formed a clear peak at pH 7.4.     

Enhancing effect of wortmannin on muscarinic stimulation of phospholipase D in rat pheochromocytoma PC12 cells.

Wortmannin, a specific inhibitor of myosin light chain kinase (MLCK), enhanced carbachol-induced formation of [3H]phosphatidylethanol ([3H]PEt), a marker of phospholipase D (PLD) activity, in [3H]palmitic acid-labeled PC12 cells. The apparent EC50 value was 1.5 microM, and the effect was maximal at 3 microM and slightly attenuated at higher concentration. Wortmannin alone had no significant effect on [3H]PEt formation. The enhancing effect of wortmannin was observed at the initial increasing phase of [3H]PEt formation but not at the subsequent plateau phase. Wortmannin enhanced also phorbol ester-induced PLD activation. Although the precise mechanism remains to be clarified, these results suggest that MLCK may be involved in PLD regulation in PC12 cells.     

Core temperature variability in diving king penguins (Aptenodytes patagonicus): a preliminary analysis

Core temperature was determined in two king penguins living in the wild at Ile de la Possession, Crozel Archipelago, using implantable four-channel temperature loggers. Core temperatures derived from bird no. 1 (sensor placed under the sternum, in the vicinity of the liver and upper stomach) were closely correlated with diving activity (as determined by an external light recorder), and ranged from 38.3°C, (on land) to a minimum of 37.2°C during a dive. Core temperatures measured in bird no. 2 showed that temperatures near the heart were generally 1°C lower than those under the sternum or in the lower abdomen. Core temperatures declined continuously during dives (by 0.8, 1.2 and 2.7°C in the lower abdomen, under the sternum and near the heart, respectively) and showed precipitous drops to 35°C, probably associated with ingestion of food. Temperatures measured near the heart fluctuated over a period of 288 s, corresponding to the duration (from the literature) of the surface/dive cycle. The relevance of these findings with respect to diving physiology, blood perfusion of tissues, tissue metabolism and aerobic dive limits is discussed.     

Structures and contribution to the antigenicity of oligosaccharides of Japanese cedar (Cryptomeria japonica) pollen allergenCry j I: relationship between the structures and antigenic epitopes of plantN-linked complex-type glycans

The oligosaccharide structures ofCry j I, a major allergenic glycoprotein ofCryptomeria japonica (Japanese cedar, sugi), were analysed by 400 MHz¹H-NMR and two-dimensional sugar mapping analyses. The four major fractions comprised a series of biantennary complex type N-linked oligosaccharides that share a fucose/xylose-containing core and glucosamine branches including a novel structure with a nongalactosylated fucosylglucosamine branch.Rabbit polyclonal anti-Cry j I IgG antibodies cross-reacted with three different plant glycoproteins having the same or shorter N-linked oligosaccharides asCry j I. ELISA and ELISA inhibition studies with intact glycoproteins, glycopeptides and peptides indicated that both anti-Cry j I IgGs and anti-Sophora japonica bark lectin II (B-SJA-II) IgGs included oligosaccharide-specific antibodies with different specificities, and that the epitopic structures against anti-Cry j I IgGs include a branch containing 1–6 linked fucose and a core containing fucose/xylose, while those against anti-B-SJA-II IgGs include nonreducing terminal mannose residues. The cross-reactivities of human allergic sera to miraculin andClerodendron Trichotomum lectin (CTA) were low, and inhibition studies suggested that the oligosaccharides onCry j I contribute little or only conformationally to the reactivity of specific IgE antibodies.Abbreviations Cry j I a major allergenic glycoprotein ofCryptomeria japonica - B-SJA-II Sophora japonica bark lectin II - CTA Clerodendron trichotomum lectin - TFMS trifluoromethanesulfonic acid - HRP horseradish peroxidase     

Porcine 80-kDa diacylglycerol kinase is a calcium-binding and calcium/phospholipid-dependent enzyme and undergoes calcium-dependent translocation.

We attempted to assess the regulatory role of EF-hand motifs recently detected in the primary structure of porcine 80-kDa diacylglycerol kinase (DGK) (Sakane, F., Yamada, K., Kanoh, H., Yokoyama, C., and Tanabe, T. (1990) Nature 344, 345-348). By using 80-kDa DGK purified from porcine thymus cytosol, we found that this isozyme indeed bound 2 mol Ca2+ per mol enzyme with high affinity (apparent dissociation constant, kd = 0.3 microM). The Ca2+ binding was cooperative with a Hill coefficient of 1.4. We next studied the effect of 1 x 10(-5) M Ca2+ on the kinetic properties of DGK employing a beta-octyl glucoside mixed micellar assay system. In the absence of Ca2+, phosphatidylserine, so far used as an enzyme activator in various assay systems, was rather inhibitory, and Ca2+ alone activated enzyme to a limited extent. However, phosphatidylserine plus Ca2+ markedly activated the enzyme, giving approximately 4-fold higher Vmax and 10-fold less Km values for ATP. In contrast, the apparent Km values for diacylglycerol were not significantly affected (approximately 3 mol %). Furthermore, by immunoblotting using anti-80 kDa DGK antibodies we found that the soluble DGK in the homogenate of porcine thymocytes was translocated to membranes in a Ca2(+)-dependent manner. Indeed we noted the presence of a 33-residue amphipathic alpha-helix in the DGK sequence, which may account for the protein-lipid interaction. The results demonstrate that Ca2+ plays a key role in the regulation of DGK action by controlling enzyme interaction with membrane phospholipids.