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161.
Pressure perturbation and differential scanning calorimetric studies of bipolar tetraether liposomes derived from the thermoacidophilic archaeon Sulfolobus acidocaldarius
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Differential scanning calorimetry (DSC) and pressure perturbation calorimetry (PPC) were used to characterize thermal phase transitions, membrane packing, and volumetric properties in multilamellar vesicles (MLVs) composed of the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius grown at different temperatures. For PLFE MLVs derived from cells grown at 78 degrees C, the first DSC heating scan exhibits an endothermic transition at 46.7 degrees C, a small hump near 60 degrees C, and a broad exothermic transition at 78.5 degrees C, whereas the PPC scan reveals two transitions at approximately 45 degrees C and 60 degrees C. The endothermic peak at 46.7 degrees C is attributed to a lamellar-to-lamellar phase transition and has an unusually low DeltaH (3.5 kJ/mol) and DeltaV/V (0.1%) value, as compared to those for the main phase transitions of saturated diacyl monopolar diester lipids. This result may arise from the restricted trans-gauche conformational changes in the dibiphytanyl chain due to the presence of cyclopentane rings and branched methyl groups and due to the spanning of the lipid molecules over the whole membrane. The exothermic peak at 78.5 degrees C probably corresponds to a lamellar-to-cubic phase transition and exhibits a large and negative DeltaH value (-23.2 kJ/mol), which is uncommon for normal lamellar-to-cubic phospholipid phase transformations. This exothermic transition disappears in the subsequent heating scans and thus may involve a metastable phase, which is irreversible at the scan rate used. Further, there is no distinct peak in the plot of the thermal expansion coefficient alpha versus temperature near 78.5 degrees C, indicating that this lamellar-to-cubic phase transition is not accompanied by any significant volume change. For PLFE MLVs derived from cells grown at 65 degrees C, similar DSC and PPC profiles and thermal history responses were obtained. However, the lower growth temperature yields a higher DeltaV/V ( approximately 0.25%) and DeltaH (14 kJ/mol) value for the lamellar-to-lamellar phase transition measured at the same pH (2.1). A lower growth temperature also generates a less negative temperature dependence of alpha. The changes in DeltaV/V, DeltaH, and the temperature dependence of alpha can be attributed to the decrease in the number of cyclopentane rings in PLFE at the lower growth temperature. The relatively low DeltaV/V and small DeltaH involved in the phase transitions help to explain why PLFE liposomes are remarkably thermally stable and also echo the proposal that PLFE liposomes are generally rigid and tightly packed. These results help us to understand why, despite the occurrence of thermal-induced phase transitions, PLFE liposomes exhibit a remarkably low temperature sensitivity of proton permeation and dye leakage. 相似文献
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Sakha BM Bhatia AK Batra VK Chaudhary VK Batra P Khurana SC 《Indian journal of experimental biology》2004,42(12):1245-1247
Mechanism of microtuberization in three elite cultivars kufri badhsha (KB), kufri chandramukhi (KCM) and kufri jawahar (KJ) of potato was studied. Sprouts of all the three cultivars were used to obtain in vitro shoot cultures. MS medium supplemented with chlorocholine chloride was found to be most suitable for all the cultivars. Maximum tuberization was obtained under incubation conditions of continuous darkness at 20 degrees +/- 1 degrees C. The highest number of micro-tubers per plant basis was produced under continuous darkness and KCM recorded the highest yield of micro-tubers and was found significantly superior to KJ and KB. 相似文献
164.
Serine proteinase inhibitors (IP’s) are proteins found naturally in a wide range of plants with a significant role in the
natural defense system of plants against herbivores. The question addressed in the present study involves assessing the ability
of the serine proteinase inhibitor in combating nematode infestation. The present study involves engineering a plant serine
proteinase inhibitor (pin2) gene into T. durum PDW215 by Agrobacterium-mediated transformation to combat cereal cyst nematode (Heterodera avenae) infestation. Putative T0 transformants were screened and positive segregating lines analysed further for the study of the stable integration, expression
and segregation of the genes. PCR, Southern analysis along with bar gene expression studies corroborate the stable integration pattern of the respective genes. The transformation efficiency
is 3%, while the frequency of escapes was 35.71%. χ2 analysis reveals the stable integration and segregation of the genes in both the T1 and T2 progeny lines. The PIN2 systemic expression confers satisfactory nematode resistance. The correlation analysis suggests that
at p < 0.05 level of significance the relative proteinase inhibitor (PI) values show a direct positive correlation vis-à-vis plant
height, plant seed weight and also the seed number. 相似文献
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The Ellis procedure of serial extraction of gonadotropins and growthhormone (GH) followed by alkaline ethanol extraction was adopted to processfreshly frozen buffalo pituitaries. The procedure after slight modificationwas found very useful as more than 2 mg of GH free immunoreactive prolactin(PRL) could be isolated from each gram of wet pituitary tissue. Further, thebiochemical purity and immunobiological potency of the extracted PRL,designated as P-I, was comparable with that of the highly purified samplesof homologous and heterologous PRLs. No non-PRL protein was detectable inP-I. Micro-heterogeneity with regard to size, charge, co- andpost-translational modifications was also investigated under differentconditions of extraction and at different stages of purification.Immunological and biological potencies were compared in homologouscompetitive enzyme linked immunosorbent assay (ELISA) developed for buffaloPRL and in rat Nb2 lymphoma proliferation assay respectively. Structuralheterogeneity was observed in all the preparations checked including freshpituitary homogenate and highly purified hormone. Nevertheless a 25 Kspecies corresponding to the hormone monomer was always the only paramountform comprising more than 90% of the total PRL protein in all thesamples including P-I. Similar size forms were observed in all preparationsand were found to be equivalents of monomers, dimers, covalent-andnon-covalent multimers, disulphide bridged forms and cleaved fragments.Other sibling species identified were glycosylated PRL, charge isoforms andforms that perhaps differed in their extractability from the pituitarytissue. Strong apparent size heterogeneity was displayed by the monomericbuffalo PRL. In light of these observations and the information on thestructural and functional significance and the consequences of polymericforms, the use of a heterogeneous PRL (P-I) as a reference hormone isrecommended for a valid assay. 相似文献
168.
The ability of ANP to inhibit the hydrolysis of phosphoinositides was examined in [3H] myoinositol-labeled intact murine Leydig tumor (MA-10) cells. Arginine vasopressin (AVP) stimulated the formation of inositol monophosphate (IP1), inositol bisphosphate (IP2), and inositol trisphosphate (IP3) both in a time- and dose- dependent manner in MA-10 cells. ANP inhibited the AVP-induced formation of IP1, IP2, and IP3 in these cells. The inhibitory effect of ANP on the AVP-stimulated formation of IP1, IP2, and IP3 accounted for 30%, 38% and 42%, respectively, which was observed at the varying concentrations of AVP. ANP caused a dose-dependent attenuation in AVP-stimulated production of IP1, IP2 and IP3 with maximum inhibition at 100 nM concentration of ANP. The production of inositol phosphates was inhibited in the presence of 8- bromo cGMP in a dose-dependent manner, whereas dibutyryl-cAMP had no effect on the generation of these metabolites. The LY 83583, an inhibitor of guanylyl cyclase and cGMP production, abolished the inhibitory effect of ANP on the AVP-stimulated production of inositol phosphates. Furthermore, 10 M LY 83583 also inhibited the ANP-stimulated guanylyl cyclase activity and the intracellular accumulation of cGMP by more than 65–70%. The inhibition of eGMP-dependent protein kinase by H-8, significantly restored the levels of AVP-stimulated inositol phosphates in the presence of either ANP or exogenous 8-bromo cGMP. The results of this study suggest that ANP exerts an inhibitory effect on the production of inositol phosphates in murine Leydig tumor (MA-10) cells by mechanisms involving cGMP and cGMP-dependent protein kinase.Established Investigator of the American Heart Association 相似文献
169.