Characterization of maltose biosynthesis from α-d-glucose-1-phosphate in Spinacia oleracea. L.

The de novo synthesis of maltose in spinach (Spinacia oleracea L.) was shown to be catalyzed by a maltose synthase, which converts two molecules of -d-glucose-1-phosphate (-G1P) (K_m 1.5 mmol l^-1) to maltose and 2 orthophosphate (Pi). This enzyme was purified 203-fold by fractionated ammonium sulfate precipitation and by column chromatography on Sepharose 6B. The addition of -G1P (15 mmol l^-1) to the isolation buffer is required to stabilize the enzyme activity during the extraction and purification procedure. Molecular weight determination by gel filtration yielded a value of 95,000. -Gluconolactone, ATP and Pi are competitive inhibitors toward the substrate -G1P. The maltose synthase catalyzes an exchange of the phosphate group of -G1P with [³²P] orthophosphate; this transfer reaction suggests that the synthesis of maltose occurs via a glucose-enzyme in a double displacement reaction. The physiological role of this enzyme as a starch initiator system is discussed.Abbreviations Fru fructose - Glc glucose - -G1P -d-glucose-1-phosphate - -G1P -d-glucose-1-phosphate - G6P d-glucose-6-phosphate This enzyme is tentatively called maltose synthase in this publication     

Dihaploids of Elymus from the interspecific crosses E. dolichatherus x E. tibeticus and E. brevipes x E. panormitanus

Summary Dihaploids (n=2x=14, SY) of two Elymus species, i.e., E. dolichatherus (Keng) Löve (2n=4x=28, SSYY) and E. brevipes (Keng) Löve (2n=4x=28, SSYY), were obtained from the interspecific hybrid combinations E. dolichatherus () x E. tibeticus (Meld.) G. Singh () and E. brevipes () x E. panormitanus (Parl.) Tzvelev (). The dihaploids were probably formed through selective elimination of male parental chromosomes in early embryo development. Meiotic chromosome behavior was studied in E. dolichatherus, E. brevipes, and their dihaploids. The two parental Elymus species had regular meioses with predominantly ring bivalent formation. A low frequency of homoeologous chromosome pairing was observed, with an average of 0.81 bivalents and 0.03 trivalents in the dihaploid of E. dolichatherus, and 0.26 bivalents in the dihaploid of E. brevipes. Up to two chromatid bridges accompanied by small fragments were present at anaphase I of the E. dolichatherus dihaploid. It is concluded from this study that: (i) both E. dolichatherus and E. brevipes are allotetraploid species; (ii) a low affinity exists between the S and Y genomes of the two Elymus species.     

Morphology of freeze-etchedTreponema refringens (Nichols)

The freeze-etch technique was used to study the morphology ofTreponema refringens (Nichols). There is a single band of cytoplasmic fibrils which follows a path in the form of a right-handed helix with a periodicity of 1500 nm around the body of the treponeme just below the cytoplasmic membrane. There are two major fracture planes, one located in the interior of the outer envelope and the second in the interior of the cytoplasmic membrane. The blebs or surface protuberances, which are quite prominent in negativestained preparations, were not evident with freeze-etch preparation, indicating they are not a part of the normal structure of this organism. The outer envelope in untreated cells was observed to closely fit the body of the treponeme, whereas the outer envelope of glutaraldehyde-treated cells had a loose, wrinkled appearance. Thus the loose-fitting outer envelope generally described for treponemes is most likely an artifact of preparation for negative-staining and thinsectioning.     

Conformational transmission in ATP synthase during catalysis: Search for large structural changes

Escherichia coli ATP synthase has eight subunits and functions through transmission of conformational changes between subunits. Defective mutation at Gly-149 was suppressed by the second mutations at the outer surface of the subunit, indicating that the defect by the first mutation was suppressed by the second mutation through long range conformation transmission. Extensive mutant/pseudorevertant studies revealed that / and / subunits interactions are important for the energy coupling between catalysis and H⁺ translocation. In addition, long range interaction between amino and carboxyl terminal regions of the subunit has a critical role(s) for energy coupling. These results suggest that the dynamic conformation change and its transmission are essential for ATP synthase.     

The effect of the methyl substituent on the bioconversion of cyclohexene derivatives

Summary The absence of the methyl substituent at the 2position of the cyclohexene ring of TCHP enhances the conversion rate as well as the yields of the 3-hydroxy product obtained byStreptomyces natalensis and the 3-keto product obtained byMycobacterium smegmatis.Abbreviations TCHP 1-(2-thienyl)-3-(1-cyclohexen-1-yl)-1-propanone - TCHP-OH 1-(2-thienyl)-3-(3-hydroxyl-1-cyclohexen-1-yl)-1-propanone - TCHP-ketone 1-(2-thienyl)-3-(1-cyclohexen-1-yl-3-one)-1-propane - TMCHP 1-(2-thienyl)-3-(2-methyl-1-cyclohexen-1-yl)-propanone     

Solution conformations of proline rings in proteins studied by NMR spectroscopy

Summary Three different conformations of proline rings in a protein in solution, Up, Down and Twist, have been distinguished, and stereospecific assignments of the pyrrolidine -, - and -hydrogens have been made on the basis of ¹H-¹H vicinal coupling constant patterns and intraresidue NOEs. For all three conformations, interhydrogen distances in the pairs -³, ³-³, ²-², ²-², and ³-³ (2.3 Å) are shorter than those in the pairs -², ²-³, ³-², ²-³, and ³-² (2.7–3.0 Å), resulting in stronger NOESY cross peaks. For the Up conformation, the ³-² and ²-³ spin-spin coupling constants are small (<3 Hz), and weak cross peaks are obtained in a short-mixing-time (10 ms) TOCSY spectrum; all other vicinal coupling constants are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. For the Down form, the -², ²-³, and ³-² vicinal coupling constants are small, leading to weak TOCSY cross peaks; all other couplings again are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. In the case of a Twist conformation, dynamically averaged coupling constants are anticipated. The procedure has been applied to bovine pancreatic trypsin inhibitor and Cucurbita maxima trypsin inhibitor-V, and ring conformations of all prolines in the two proteins have been determined.     

Silver nitrate and aminoethoxyvinylglycine affect <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated apple transformation

In Fuji, the production of ethylene was increased with the addition of AgNO₃ and inhibited with the addition of 10 M aminoethoxyvinylglycine (AVG). The addition of 80 M AgNO₃ to transformed explants of Fuji cultured on selection medium resulted in increased ethylene production (20 l l^–1) at 3 weeks. Under examining the effect of AgNO₃ in Fuji, the 40 M AgNO₃ showed with higher 33.8% and 6.5% in the efficiency of regeneration and transformation. However, ethylene production in Gala explants treated with 10M AgNO₃ (3 l l^–1) decreased after 2 weeks compared with the control (5 l l^–1). Although the regeneration efficiency of Gala with 10 M AgNO₃ was higher (41.1%) than the control (20.1%), there was no significant difference in the transformation efficiency at the same concentration. Shoot regeneration of Fuji and Gala was completely inhibited with 10 M AVG. These results suggest that the addition of AgNO₃ affects the efficiency of Agrobacterium-mediated gene transfer in Fuji.Eun Soo Seong, Ill Min Chung- These two Authors Contributed equally to this work     

Combined use of radioimagers and radioactive 3′OH DNA nick end labelling to quantify apoptosis in cell lines and tissue sections: applications to virus-induced apoptosis

DNA fragmentation is a key feature of the degradation phase of apoptosis. In this work we have developed an assay, based on radioimager (-IMAGER and -IMAGER) quantification of radioactive nick end labelling (RANEL), which is quantitative, rapid and sensitive to study in vitro and in vivo induced apoptosis. To establish the technique, in vitro apoptosis of T cell lines was induced by stimulation of the Fas receptor; cells were labelled using TdT-mediated [-³³P] dCTP nick end labelling, after which then radioactivity was quantified using a -IMAGER. We have also shown that the RANEL method can be applied to the quantification and visualisation, by -IMAGER analysis, of liver tissue sections from mouse Fas-induced fulminant hepatitis or from Dengue-1 virus infected individuals. Finally, this system has also been used to detect apoptosis induced by rabies virus in Jurkat T cells. These data have established a large field of application for the RANEL assay.     

Ultrastructural localization of gonadotrophic hormones in the porcine pituitary using the immunoperoxidase technique

Summary Using specific antibodies against subunits of porcine LH and FSH, the pituitary cells which produce these two gonadotrophins were identified in the porcine pituitary at the ultrastructural level using the immunoperoxidase technique. It was clearly shown that most of the gonadotrophic cells are responsible for the production of both FSH and LH. However, some cells, only positive for FSH or LH, indicate that the concentrations of FSH and LH vary from cell to cell. At the ultrastructural level, the FSH/LH cells contain one class of secretory granules strongly positive for both FSH and LH as well as large negatively stained dense bodies. These findings indicate that the one cell-one hormone concept may not apply to gonadotrophic hormones; a FSH/LH cell cannot be distinguished from a LH or a FSH cell without immunocytochemical identification of its hormonal content.Abbreviations p-LH porcine luteinizing hormone - p-LH porcine LH subunit - p-LH porcine LH subunit - p-FSH porcine follicule stimulating hormone - p-FSH porcine FSH subunit - b-TSH bovine thyrotropic hormone     

Synthesis of polygalacturonase during tomato fruit ripening

The cell wall degrading enzyme polygalacturonase (E.C. 3.2.1.15) is not detectable in green tomatoes (Lycopersicon esculentum Mill). Activity appears at the onset of ripening and in ripe fruit it is one of the major cell-wall-bound proteins. Radioimmunoassay results, employing an antibody against purified polygalacturonase, suggest that during ripening the enzyme is synthesised de novo. Radioimmunoassay data also show that the low level of polygalacturonase in Never ripe mutants and the lack of activity in ripening inhibitor mutants can be correlated to the levels of immunologically detectable polygalacturonase protein.Abbreviations PG polygalacturonase - Nr Never ripe mutation - rin ripening inhibitor mutation     

Heterogeneous binding and killing behaviour of human γ/δ-TCR+ lymphokine-activated killer cells against K562 and Daudi cells

Effector-target conjugates, formed by coincubation of lymphokine-activated killer (LAK) cells with either K562 or Daudi cells, were separated from single cells by Percoll sedimentation. The occurrence of various CD molecules (CD3, CD56, CD57, CD16, /-TCR) was compared in both fractions. Only LAK cells expressing the / T cell receptor (TCR) were found in a significantly increased percentage in fractions containing conjugates indicating that /-TCR⁺ LAK cells were preferably bound to target cells at the time of separation. In order to determine whether /-TCR⁺ LAK cells also show a preferred killing activity against the targets, cultures enriched with or depleted of /-TCR⁺ cells were established. Against K562 cells, /-TCR⁺-enriched cultures showed a greatly reduced killing activity compared to LAK bulk cultures or cultures depleted of /-TCR⁺ cells. Using Daudi cells as targets the enriched fraction revealed a slightly increased killing activity compared to bulk cultures or depleted fractions. Preincubation of /-TCR⁺ LAK cells with anti-/ or anti-CD3 mAb resulted in a distinct increase of the killing activity against K562 cells, but in only a slightly enhanced activity against Daudi cells. It is postulated that /-TCR⁺ LAK cells use the same adhesion mechanism for both targets but that only Daudi cells express a specific ligand for the /-TCR. Occupation of the /-TCR/CD3 complex by mAb, however, seems to substitute for the absent epitope on K562 cells by eliciting stimulatory signals in /-TCR⁺ LAK cells which, in combination with the binding stimulus, trigger cytolytic activity.This work was supported by the Hartmann-Müller Foundation, Zürich     

Effect of serum type and concentration on the expression ofβ-galactosidase in recombinant vaccinia virus infected HeLa S3 cells

The effect of serum type and concentration on recombinant protein expression in vaccinia virus infected HeLa S3 cells was studied in both static and suspension culture. A model heterologous protein,-galactosidase (-gal), was used. Calf and horse sera in the range of 0.5–10%(v/v) were investigated. In static culture, the calf serum concentration did not show any significant influence on the -gal production which was almost completed within 24h postinfection (pi). Higher horse serum concentration, on the other hand, resulted in higher -gal concentration which continued to increase until 48 h pi. Total -gal concentrations in 0.5% calf serum at 24 h pi and 10% horse serum at 48 h pi were 2.2±0.7 and 2.2±0.1 IU/ml, respectively. In suspension culture, both sera showed their respective effects on the -gal production similar to those observed in static culture, indicating that the cultivation method had little influence on -gal production. Accordingly, the use of 0.5% calf serum after virus infection in recommended for economical -gal production.     

β-Adrenoceptors in the Tree Shrew Brain. I. Distribution and Characterization of [125I]Iodocyanopindolol Binding Sites

1. The number and distribution pattern of -adrenergic receptors in the brain have been reported to be species specific. The aim of the present study was to describe binding of the -adrenoceptor ligand [¹²⁵I]iodocyanopindolol in the brain of the tree shrew (Tupaia belangeri), a species which provides an appropriate model for studies of psychosocial stress and its consequences on central nervous processes.2. ¹²⁵I-Iodocyanopindolol (¹²⁵ICYP) labeling revealed a high degree of nonspecific binding, which was due mainly to interactions of this ligand with serotonin binding sites. For a quantitative evaluation of ₁- and ₂-adrenoceptors, serotonin binding sites had to be blocked by 100 M 5HT.3. Binding of the radioligand to ₁- and ₂-adrenoceptors was characterized using the ₁-specific antagonist CGP20712A and the ₂-specific antagonist ICI118.551. ₁-adrenoceptor binding is present in the whole brain, revealing low receptor numbers in most brain regions (up to 1.5 to 2.7 fmol/mg). A slight enrichment was observed in cortical areas (lateral orbital cortex: 4.0±0.7 fmol/mg) and in the cerebellar molecular layer (8.7±1.0 fmol/mg).4. Competition experiments demonstrated high- and low-affinity binding sites with considerable variations in K _i values for CGP20712A, showing that various affinity states of ₁-adrenoceptors are present in the brain (K _i: 0.61 nM to 67.1 M). In the hippocampus, only low-affinity ₁-adrenoceptors were detected (K _i: 1.3±0.2 M). Since it is known that ¹²⁵ICYP labels not only membrane bound but also internalized -adrenoceptors, it can be assumed that the large population of the low-affinity sites represents internalized receptors which may be abundant due to a high sequestration rate.5. High numbers of ₂-adrenoceptors are present in only a few brain structures of tree shrews (external layer of the olfactory bulb, 15.8±2.0 fmol/mg; claustrum, 19.3±1.5 fmol/mg; anteroventral thalamic nucleus, 19.4±1.5 fmol/mg; cerebellar molecular layer, 55.0±4.3 fmol/mg). Also for this class of -adrenoceptors, high- and low-affinity binding sites for the ₂-selective antagonist ICI118.551 were observed, indicating that ¹²⁵ICYP labels membrane bound and internalized ₂-adrenoceptors. Only in the cerebellar molecular layer was a high percentage of high-affinity ₂-adrenoceptors detected (K _i for ICI118.551 was 1.8±0.3 nM for 90% of the receptors).6. In conclusion, ₁- and ₂-adrenoceptor binding can be localized and quantified by in vitro receptor autoradiography in the brains of tree shrews when serotonergic binding sites are blocked. Modulatory effects of long-term psychosocial conflict on the central nervous -adrenoceptor system in male tree shrews are described in the following paper.     

Primary structures of alpha- and beta-subunits of alpha-amylase inhibitors from seeds of three cultivars of Phaseolus beans

The primary structures of three -amylase inhibitors (TAI, DAI, and MAI-2) consisting of glycoprotein subunits and from the respective seeds of three cultivars of Phaseolus beans, Toramame (Phaseolus vulgaris L.), Daifukumame (Phaseolus vulgaris L.), and Murasakihanamame (Phaseolus coccineus L.) were determined by sequencing the peptide fragments derived from their enzymatic digestions. Major sugar chains of the inhibitors were also assessed by analyzing glycopeptides in the enzymatic digests. The subunits, and , were shown to be composed of 76 and 139 amino acid residues, respectively, in each inhibitor. The overall amino acid sequences of the inhibitors were slightly different from one another. Furthermore, the sequence of TAI was the same as that deduced from a cDNA clone encording -amylase inhibitor-1 from the common bean (Phaseolus vulgaris L.). It was also revealed that there were two N-glycosylation sites in each -subunit: PA-derivatives of the major N-glycans were estimated to be M6B at Asn(12) and M9A at Asn(65). Each -subunit of TAI and MAI-2 had two N-glycosylation sites, while the -subunit of DAI had only one site. The major N-glycans pyridylaminated were estimated to be M3X at Asn(63) in each -subunit and M3FX at Asn(83) in -subunits of TAI and MAI-2.     

Secretion of glycosylated human recombinant haptoglobin in Baculovirus-infected insect cells

Human haptoglobin (Hp²) was synthesized in insect cells using the baculovirusAutographa california nuclear polyhedrosis virus (AcNPV) as an expression vector. Viruses carrying the proHp² cDNA, either fused or non fused to viral polyhedrin DNA sequences, expressed intracellularly low levels of unglycosylated and non maturated haptoglobin. On the contrary, recombinant viruses containing the preoroHp² cDNA directed the expression of high levels of prohaptoglobin. To a large extent, the uncleaved product was found in the culture medium as a glycosylated molecule. Despite the lack of maturation into subunits, the secreted recombinant prohaptoglobin was able to bind hemoglobin in vitro, although less efficiently than plasma-derived haptoglobin.     

Factors influencing synthesis and activity of β-galactosidase inLactobacillus acidophilus

Summary In the type-strainLactobacillus acidophilus ATCC 4356 -galactosidase (-gal) was inducible; lactose, galactose, melibiose and probably maltose, but not glucose, fructose, mannose, sucrose and cellobiose, induced -gal synthesis. Glucose partially inhibited -gal-induction by lactose but not by isopropyl--D-thiogalactoside. -gal synthesis during cell growth was maximal at 0.4% lactose, stimulated by Ca²⁺ but inhibited by Mg²⁺ and Mn²⁺. -gal in the cell-free extract had optimum activity at pH 6.5 and at 45°C. The enzyme activity was stimulated by Mg²⁺, inhibited by Ca²⁺, destroyed by oxidizing agents and protected by reducing agents.     

Control of glycoprotein synthesis: substrate specificity of rat liver UDP-GlcNAc:Manα3R β2-N-acetylglucosaminyl-transferase I using synthetic substrate analogues

UDP-GlcNAc: Man3R 2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) is the key enzyme in the synthesis of complex and hybrid N-glycans. Rat liver GlcNAc-T I has been purified more than 25,000-fold (M _r 42,000). TheV _max for the pure enzyme with [Man6(Man3)Man6](Man3)Man4GlcNAc4GlcNAc-Asn as substrate was 4.6 µmol min^–1 mg^–1. Structural analysis of the enzyme product by proton nuclear magnetic resonance spectroscopy proved that the enzyme adds anN-acetylglucosamine (GlcNAc) residue in 1–2 linkage to the Man3Man-terminus of the substrate. Several derivatives of Man6(Man3)Man-R, a substrate for the enzyme, were synthesized and tested as substrates and inhibitors. An unsubstituted equatorial 4-hydroxyl and an axial 2-hydroxyl on the -linked mannose of Man6(Man3)Man-R are essential for GlcNAc-T I activity. Elimination of the 4-hydroxyl of the 3-linked mannose (Man) of the substrate increases theK _M 20-fold. Modifications on the 6-linked mannose or on the core structure affect mainly theK _M and to a lesser degree theV _max, e.g., substitutions of the Man6 residue at the 2-position by GlcNAc or at the 3- and 6-positions by mannose lower theK _M, whereas various other substitutions at the 3-position increase theK _M slightly. Man6(Man3)4-O-methyl-Man4GlcNAc was found to be a weak inhibitor of GlcNAc-T I.Abbreviations BSA Bovine serum albumin - Bn benzyl - Fuc, F l-fucose - Gal, G d-galactose - GalNAc, GA N-acetyl-d-galactosamine - Glc d-glucose - GlcNAc, Gn N-acetyl-d-glucosamine - HPLC high performance liquid chromatography - Man, M d-mannose - mco 8-methoxycarbonyl-octyl, (CH₂)₈ COOOCH₃ - Me methyl - MES 2-(N-morpholino)ethanesulfonate - NMR nuclear magnetic resonance - PMSF phenylmethylsulfonylfluoride - pnp p-nitrophenyl - SDS sodium dodecyl sulfate - T transferase - Tal d-talose - Xyl d-xylose; - {0, 2 + F} Man6 (GlcNAc2Man3) Man4GlcNAc4 (Fuc6) GlcNAc - {2, 2} GlcNAc2Man6 (GlcNAc2Man3) Man4GlcNAc4GlcNAc; M₅-glycopeptide, Man6 (Man3) Man6 (Man3) Man4 GlcNAc4GlcNAc-Asn Enzymes: GlcNAc-transferase I, EC 2.4.1.101; GlcNAc-transferase II, EC 2.4.1.143; GlcNAc-transferase III, EC 2.4.1.144; GlcNAc-transferase IV, EC 2.4.1.145; GlcNAc-transferase V, UDP-GlcNAc: GlcNAc2 Man6-R (GlcNAc to Man) 6-GlcNAc-transferase; GlcNAc-transferase VI, UDP-GlcNAc: GlcNAc6(GlcNAc2) Man6-R (GlcNAc to Man) 4-GlcNAc-transferase; Core 1 3-Gal-transferase, EC 2.4.1.122; 4-Gal-transferase, EC 2.4.1.38; 3-Gal-transferase, UDP-Gal: GlcNAc-R 3-Gal-transferase; blood group i 3-GlcNAc-transferase, EC 2.4.1.149; blood group I 6-GlcNAc-transferase, UDP-GlcNAc: GlcNAc3Gal-R (GlcNAc to Gal) 6-GlcNAc-transferase.     

A comparative assessment of TLC overlay technique and microwell adsorption assay in the examination of influenza A and Sendai virus specificities towards oligosaccharides and sialic acid linkages of gangliosides

Influenza A and Sendai viruses bind toneolacto-series gangliosides isolated from human granulocytes. Differences in receptor specificity of influenza viruses A/PR/8/34 (H1N1), A/X-31 (H3N2), and parainfluenza Sendai virus (HNF1, Z-strain) were determined by two direct solid phase binding assays: the overlay technique, which combines high-resolution in the separation of gangliosides on thin-layer chromatograms with direct binding; and the microwell adsorption assay as a convenient binding assay which is performed in microtitre wells to estimate the avidity of binding to an isolated ganglioside. Both methods were applied for comparative binding studies. Viruses were found to exhibit specificity for oligosaccharides and sialic acids as well as for chain length of the neutral carbohydrate backbone, whereas differing fatty acids (C_24:1 and C_16:0) in the ceramide portion had no impact on virus adsorption. Terminal sialyloligosaccharides Neu5Ac2-3Gal1-4Glc-R of G_M3, and Neu5Ac2-3Gal1-4GlcNAc-R as well as Neu5Ac2-6Gal1-4GlcNAc-R ofneolacto-series gangliosides with nLcOse₄Cer and nLcOse₆Cer backbone, exhibited significant specific receptor activity towards the different viruses. To compare the data revealed from both test systems, values of virus binding were ascertained by a non-parametric statistical approach based on rank correlation. The rank correlation coefficientr _s was calculated according to Spearman from each virus binding towards G_M3, IV³Neu5Ac-nLcOse₄Cer, IV⁶Neu5Ac-nLcOse₄Cer and VI³Neu5Ac-nLcOse₆SCer. The rank correlation coefficients 0.74, 0.95 and 0.92, which were determined for A/PR/8/34 (H1N1), A/X-31 (H3N2) and Sendai virus (HNF1, Z-strain), respectively, indicated that both assays generate highly correlated experimental data. Based on these results, analyses of virus binding on thin-layer chromatograms as well as in microwells were found equivalent tools for ganglioside receptor studies. Abbreviations: BSA, bovine serum albumin; GSL(s), glycosphingolipids; HPTLC, high performance thin-layer chromatography; PBS, phosphate buffered saline; Neu5Ac,N-acetylneuraminic acid [35];r _s = rank correlation coefficient according to Spearman. The designation of the glycosphingolipids follows the IUPAC-IUB recommendations [36]. LacCer or lactosylceramide, Gal1-4Glc1-1Cer; lacto-N-neotetraosylceramide or nLcOse₄Cer, Gal1-4GlcNAc1-3Gal1-4Glc1-1Cer; lacto-N-norhexaosylceramide or nLcOse₆Cer, Gal1-4GlcNAc1-3Gal1-4GlcNAc1-3Gal1-4Glc1-1Cer; G_M3 (according to Svennerholm [37]) or II³Neu5AcLacCer.     

A coupled pacemaker-slave model for the insect photoperiodic clock: interpretation of ovarian diapause data in Drosophila melanogaster

A coupled circadian oscillator model for the insect photoperiodic clock is described which consists of a hierarchically arranged pacemaker and slave. The pacemaker is self-sustained, temperature compensated, and entrainable by the light cycle; the slave is a damping oscillation receiving entrainment from two sources, from the pacemaker via a coupling factor, and also directly from the light. The damping slave oscillation is seen as the photoperiodic oscillator, equivalent to that proposed earlier by Lewis and Saunders (1987). The present simulations describe the effect of the strength of the coupling factor between hypothetical short- and long-period pacemaker oscillations (modelled on the clock mutants per ^sand per ^L2in Drosophila melanogaster) and a slave oscillation with a period of about 24 hours. The output is presented in terms of photoperiodic response curves and Nanda-Hamner, or resonance, plots. With a high coupling strength, the pacemakers strongly entrain the slave, but with a low coupling strength the slave's properties are more evident. The model is presented as a possible explanation for recent ovarian diapause data in D. melanogaster clock mutants (Saunders 1990), but also as a more general model for the role of the insect circadian system in seasonal time measurement.