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1.
The biosynthesis of riboflavin precursor 6,7-dimethyl-8-ribityllumazine was studied in extracts of Pichia guilliermondii yeast mutants of rib5 and rib6 genotypes with impaired synthesis of proteins P1 and P2, respectively. It was shown that synthesis of 6,7-dimethyl-8-ribityllumazine took place in extracts of rib5 mutant (active P1 protein) in the presence of 2,4-dihydroxy-5-amino-6-ribitylaminopyrimidine and the compound formed from ribose-5-phosphate by extracts of rib6 mutant (active P2 protein). No lumazine was formed in extracts of rib6 mutant from pyrimidine substrate and ribose-5-phosphate preincubated with extracts of rib5 mutant. Hence, P1 protein (the product of RIB5 gene) participates in the biosynthesis of 6,7-dimethyl-8-ribityllumazine from 2,4-dihydroxy-5-amino-6-ribitylaminopyrimidine and aliphatic intermediate which is formed from ribose-5-phosphate, under the action of P2 protein (the product of RIB6 gene). 相似文献
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Paraskeva Michailova Ninel Petrova Lillian Ramella Gabriella Sella Jordanka Todorova Vincenzo Zelano 《Genetica》1996,98(2):161-178
A population of Chironomus riparius from a Po river station near Moncalieri (a trace-metal polluted station) was studied. In this population was established a great variability of band structure of polytene chromosomes as well as paracentric heterozygous inversions, deletions, deficiencies, partial breaks, diploid chromosome fragments, and changes in functional activity and appearance of heterochromatin. In arms A through F, some bands had an increased size compared to the standard chromosomic map. Some bands appeared in a heterozygous or normal homozygous state or were amplified. In all arms, many condensed stable bands appeared in the decondensed state when compared to the standard map. Asynaptic zones in arms E and G as well as heterozygous Balbiani rings and NORs were established. Very often the 4th chromosome was almost completely heteropycnotic and looded like a pompon chromosome. For the first time in this species, a high frequency of ectopic pairings of different arms was observed. Telomeric regions involved in ectopic pairings had a granular appearance, as did some centromeres. The hypothesis is advanced that such a high frequency of structural rearrangements could be correlated with genomic distribution of specific mobile elements. 相似文献
4.
Reconstituted Na+,K+-ATPase from either pig kidney or shark rectal glands was phosphorylated by cAMP dependent protein kinase, PKA. The stoichiometry was 0.9 mole Pi/mole -subunit in the pig kidney enzyme and 0.2 mol Pi/mol -subunit in the shark enzyme. In shark Na+,K+-ATPase PKA phosphorylation increased the maximum hydrolytic activity for cytoplasmic Na+ activation and extracellular K+ activation without affecting the apparent Km values. In contrast, no significant functional effect after PKA phosphorylation was observed in pig kidney Na+,K+-ATPase. 相似文献
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G. S. Voronov M. S. Berezhetskii Yu. F. Bondar’ I. Yu. Vafin D. G. Vasil’kov E. V. Voronova S. E. Grebenshchikov I. A. Grishina N. F. Larionova A. A. Letunov V. P. Logvinenko A. I. Meshcheryakov E. I. Pleshkov Yu. V. Khol’nov O. I. Fedyanin V. A. Tsygankov S. V. Shchepetov V. A. Kurnaev I. V. Vizgalov V. A. Urusov I. A. Sorokin F. S. Podolyako A. Antipenkov R. Pearce L. Worth 《Plasma Physics Reports》2013,39(4):277-288
Results are presented from L-2M stellarator experiments on testing a possible method for detection of water microleakages in the cooling system of the first wall and vacuum chamber of ITER. The method consists in the spectroscopic detection of spectral lines of the OH hydroxyl, which forms via the dissociation of water molecules in plasma. Emission in the spectral band of 305–310 nm can be detected even at water leakage rates less than 10?4 Pa m3/s. Chemical reactions between water and boron compounds on the vacuum chamber wall delay the detection of leakages up to ~2000 s. A similar phenomenon can be expected when a leakage will occur in ITER, where the materials suggested for the first wall (Be, Li) can also chemically react with water. 相似文献
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Belyavskaya NA 《Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology》2002,9(1):P221-P222
A study to investigate the effects of La" ions on graviresponsiveness, statocyte ultrastructure, and calcium balance were carried out on 5-day seedlings of Pisum sativum. The results indicate that this blocker of some Ca2+ channels 1) inhibits the root graviresponsiveness, 2) disturbs statocyte polarity and changes qualitative and quantitative characteristics of some cellular organelles and compartments, 3) results in the disturbance of calcium homeostasis. Taken together, the data are consistent with the hypothesis, concerning the role of Ca2+ in gravitational signal transduction. 相似文献
9.
G. S. Voronov D. K. Akulina G. M. Batanov M. S. Berezhetskii D. G. Vasil’kov I. Yu. Vafin E. V. Voronova S. E. Grebenshchikov I. A. Grishina L. V. Kolik N. F. Larionova V. P. Logvinenko D. V. Malakhov A. I. Meshcheryakov Yu. I. Nechaev A. E. Petrov K. A. Sarksyan V. V. Saenko N. N. Skvortsova O. I. Fedyanin N. K. Kharchev Yu. V. Khol’nov S. V. Shchepetov 《Plasma Physics Reports》2010,36(7):551-557
A plasma confinement mode characterized by the formation of an edge transport barrier (ETB) was discovered in the L-2M stellarator after boronization of the vacuum vessel wall. The transition into this mode is accompanied by a jump in the electron temperature by 100–200 eV at the plasma edge and a sharp increase in the gradient of the electron temperature T e in this region. The threshold power for the transition into the ETB confinement mode with an increased electron temperature gradient is P thr ?Te = (60 ± 15)n e [1019 m?3] kW. The formation of the ETB manifests itself also in a substantial change in the electron density profile. A density peak with a steep gradient at the outer side forms at the plasma edge. The threshold power for the transition into the ETB confinement mode corresponding to a substantial increase in the plasma density gradient near r = a is P thr ?Te = (67 ± 9)n e [1019 m?3] kW, which agrees to within experimental error with the threshold power for the transition into the ETB confinement mode determined from the sharp increase in the gradient of the electron temperature T e . The value of P thr for the L-2M stellarator agrees to within 25% with that obtained from the tokamak scaling. In the ETB confinement mode, the plasma energy W and the energy confinement time τ E determined from diamagnetic measurements increase by 20–30% as compared to those obtained from the stellarator scaling for the confinement mode without an ETB. When the heating power increases by a factor of 2–3 above the threshold value, the effects related to improved energy confinement disappear. 相似文献
10.
In the nurse plant syndrome, or nurse association, seedlings (beneficiaries) are associated with adult shrubs/trees (benefactors).
This phenomenon has been documented in several regions of the planet. Abiotic stress amelioration (one mechanism of facilitation)
is one of the causes of this association. Most of the studies addressing the nurse syndrome have been conducted on spatial
scales of a few hectares and have focused on only one or a few species. Moreover, there is an almost complete lack of studies
addressing the incidence and characteristics of the nurse phenomenon in the arid Andes of South America. We undertook a first
approximation to the study of facilitation in these ecosystems. The study was conducted at local and regional scales and involved
the assessment of the spatial distribution of juveniles (seedlings and saplings) of 51 populations of 16 shrub and 12 cactus
species in relation to shrub cover at 20 localities of the Prepuna (subtropical Andes of Bolivia and Argentina, 20–26°S).
In terms of spatial distribution, the juveniles of most of the populations of shrubs studied were distributed both under the
shrubs and in open spaces, thereby showing an apparent indifference to microhabitat. Globose and opuntioid cacti were preferentially
distributed below the canopies of shrubs and were usually more associated with the dominant shrub species, which stood out
as better potential nurses. The pattern was consistent throughout the region, including the more mesic and arid localities.
The fact that Prepuna woody species are capable of establishing in open spaces would confer this region a greater resilience.
Our findings further suggest that community dynamics in arid and semi-arid environments are more variable than previously
thought. 相似文献