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PubMed2025

Combined Evidence Reveals the Origin of a Rapid Range Expansion Despite Retained Genetic Diversity and a Weak Founder Effect.

Many species are currently experiencing range shifts in response to changing environmental conditions with potentially serious genetic consequences. Repeated founder events and strong genetic drift are expected to erode genetic variation at the range front, reducing adaptive potential and slowing or even halting the expansion. However, the severity of these consequences for common and highly mobile species undergoing environment-driven range shifts (c.f. invasions) is less clear. Here, we combined historical observations and contemporary movement data of the common reed warbler (Acrocephalus scirpaceus) with genomic evidence from across its European breeding range to (1) infer the origin and (2) quantify the genetic consequences of a recent and rapid northward range expansion. Although there were no reductions in levels of nucleotide diversity or allelic richness, nor a signal of founder effect in the directionality index (ψ), our combined dataset approach was able to infer an expansion origin from the southwest. Furthermore, we found that private allelic richness retained a slight but significant linear decline along the colonisation route. These results suggest that high dispersal capabilities can allow even philopatric species to avoid the loss of genetic diversity during rapid range expansions. Nevertheless, if multiple lines of evidence enable identification of an expansion pathway, we may still detect genetic signals of expansion.

Founder Effect↗

PubMed2026

Beyond species trees: pervasive gene flow limits phylogenomic resolution in the diversification of Juniperus from the Qinghai-Tibet Plateau.

Understanding how lineages diversify despite persistent ancestral polymorphism and recurrent gene flow remains a central challenge in evolutionary biology. Juniperus distributed across the Qinghai-Tibet Plateau provide an ideal system for addressing this question because repeated geological uplift and climatic oscillations have likely promoted cycles of lineage divergence, range shifts, and secondary contact. Here, we combined approximately 1.08 million genome-wide SNPs from 164 individuals representing thirteen Juniperus lineages with phylogenomic datasets comprising 3,381 nuclear single-copy genes and nearly complete plastomes. We detected extensive phylogenomic discordance and cytonuclear incongruence across genomic datasets. Topology weighting, coalescent simulations, quartet-based tests, and analyses of gene flow and reticulation collectively support the interpretation that these patterns were shaped by the combined effects of prolonged incomplete lineage sorting and gene flow during lineage diversification. Ecological niche analyses further provide a spatial and climatic context in which environmentally similar lineages may have had greater opportunities for secondary contact during historical range shifts. Collectively, our results reveal that the evolutionary history of Qinghai-Tibet Plateau Juniperus is characterized by reticulate diversification rather than strictly bifurcating evolution, and demonstrate how genome-wide discordance can provide biological insights into the evolutionary processes underlying lineage diversification.

Gene Flow↗

PubMed1979

Auditory nerve activity and cochlear morphology after noise exposure.

Four chinchillas were exposed for 5 days to an octave band of noise centered at 4 kHz and having an SPL of 86 dB. After a recovery period of approximately 6 months, behavioral audiograms were obtained and auditory nerve fiber activity was recorded. The animals were killed and the cochleas embedded in plastic to obtain a surface preparation and 1 mu radial sections of the organ of Corti. Behavioral threshold shifts ranged from 5 to 20 dB at frequencies between 4 and 11 kHz. Auditory nerve fiber thresholds were elevated up to 70 dB for units with characteristic frequencies between 4 and 14 kHz. Units with higher and lower characteristic frequencies had normal thresholds. Cochleagrams showed narrow lesions of inner and/or outer hair cells over approximately a 1 mm distance. A comparison of the three realms of data revealed the following: (1) The greatest threshold shifts from the noise exposure were seen in the single nerve fiber thresholds while the smallest shifts were seen in the behavioral thresholds, (2) the greatest behavioral and neural threshold shifts and greatest cochlear damage occurred 1 octave above the center frequency of the noise exposure, and (3) based on the frequency-place map of the chinchilla cochlea, the range of fibers with elevated thresholds exceeded the extent of the OHC lesion. A number of anatomical changes were seen that effectively increased the extent of the damage found in the chochleagram. These changes included: distortions in the surface topography of the organ of Corti affecting the orientation of IHC; missing pillar cells in the presence of normal OHC and/or IHC and protrusion of the IHC cuticular plate into the subtectorial space.

Animals↗

PubMed2025

Genomic and morphological analysis reveals long-term mammoth hybridization in British Columbia, Canada.

Climate changes profoundly impact species distributions and can drastically alter dynamics between formerly isolated taxa. The evolution of mammoths within North America was characterized by repeated cycles of dispersal and putative gene flow between woolly and Columbian mammoths. However, as genome-wide studies on mammoths have predominantly focused on Siberia, the consequences of these North American range shifts remain unclear. Here, we generated genome-wide and morphological data for two Late Pleistocene mammoth molars from British Columbia, Canada (BC), and jointly analysed these with previously published data. Our genome-wide analysis (n = 16) revealed gene flow between woolly and Columbian mammoths that would have gone undiscovered based on morphological (n = 48) and mitochondrial analysis (n = 124) alone. Consistent with their hybrid nature, our analyses suggest that these two BC mammoths had elevated genomic diversity. Our results highlight the importance of combining data types to reconstruct past evolutionary events. These findings demonstrate how the geographical range expansion of woolly mammoths resulted in long-term hybridization with local Columbian mammoths and enhance our understanding of the genomic and morphological consequences of climate-mediated dispersal.

British Columbia↗

PubMed1978

Analyses of absorption and fluorescence spectra of water-soluble chlorophyll proteins, pigment system II particles and chlorophyll a in diethylether solution by the curve-fitting method.

Absorption and fluorescence spectra in the red region of water-soluble chlorophyll proteins, Lepidium CP661, CP663 and Brassica CP673, pigment System II particles of spinach chloroplasts and chlorophyll a in diethylether solution at 25 degrees C were analyzed by the curve-fitting method (French, C.S., Brown, J.S. and Lawrence, M.C. (1972) Plant Physiol 49, 421--429). It was found that each of the chlorophyll forms of the chlorophyll proteins and the pigment System II particles had a corresponding fluorescence band with the Stokes shift ranging from 0.6 to 4.0 nm. The absorption spectrum of chlorophyll a in diethylether solution was analyzed to one major band with a peak at 660.5 nm and some minor bands, while the fluorescence spectrum was analyzed to one major band with a peak at 664.9 nm and some minor bands. A mirror image was clearly demonstrated between the resolved spectra of absorption and fluorescence. The absorption spectrum of Lepidium CP661 was composed of a chlorophyll b form with a peak at 652.8 nm and two chlorophyll a forms with peaks at 662.6 and 671.9 nm. The fluorescence spectrum was analyzed to five component bands. Three of them with peaks at 654.8, 664.6 and 674.6 nm were attributed to emissions of the three chlorophyll forms with the Stokes shift of 2.0--2.7 nm. The absorption spectrum of Brassica CP673 had a chlorophyll b form with a peak at 653.7 nm and four chlorophyll a forms with peaks at 662.7, 671.3, 676.9 and 684.2 nm. The fluorescence spectrum was resolved into seven component bands. Four of them with peaks at 666.7, 673.1, 677.5 and 686.2 nm corresponded to the four chlorophyll a forms with the Stokes shift of 0.6--4.0 nm. The absorption spectrum of the pigment System II particles had a chlorophyll b form with a peak at 652.4 nm and three chlorophyll a forms with peaks at 662.9, 672.1 and 681.6 nm. The fluorescence spectrum was analyzed to four major component bands with peaks at 674.1, 682.8, 692.0 and 706.7 nm and some minor bands. The former two bands corresponded to the chlorophyll a forms with peaks at 672.1 and 681.6 nm with the Stokes shift of 2.0 and 1.2 nm, respectively. Absorption spectra at 25 degrees C and at --196 degrees C of the water-soluble chlorophyll proteins were compared by the curve-fitting methods. The component bands at --196 degrees C were blue-shifted by 0.8--4.1 nm and narrower in half widths as compared to those at 25 degrees C.

Chlorophyll↗

PubMed2025

Historical introgression as a driver of diversification of diploid Picris (Compositae) in the Mediterranean Basin.

The Mediterranean Basin is recognized as one of the world's most prominent biodiversity hotspots, where past climatic changes have driven range shifts, secondary contact between populations, and gene exchange. This study investigates the impact of historical introgression on the diversification of diploid members of the genus Picris (Compositae). Using nuclear and plastid genome data obtained through the Hyb-Seq approach, we assess whether introgression contributed to the evolution of the Mediterranean Picris, potentially giving rise to multiple regional endemics. We also test whether introgression was associated with the transfer of traits such as life strategy and fruit morphology, which are involved in habitat-specific adaptation. Phylogenetic network analysis revealed two major introgression events that shaped evolutionary trajectories within the genus. The earliest and most complex events involved the Turkish endemic P. campylocarpa, which hybridized with the most recent common ancestor (MRCA) of the P. cyprica-P. pauciflora lineage and with the MRCA of the B1 subclade, comprising the P. hieracioides group and the P. scaberrima-P. strigosa lineage. The latter introgression preceded shifts from iteroparity to semelparity and from heterocarpy to homocarpy, ruling out an adaptive introgression origin for these traits. Nevertheless, all detected historical introgression events contributed to the diversification of diploid Picris taxa.

Diploidy↗

PubMed1975

Studies of individual carbon sites of proteins in solution by natural abundance carbon 13 nuclear magnetic resonance spectroscopy. Strategies for assignments.

Natural abundance 13C Fourier transform NMR spectra (at 15.18 MHz, in 20-mm sample tubes) of aqueous native proteins yield numerous narrow single carbon resonances of nonprotonated aromatic carbons. Techniques for the assignment of these resonances are presented. Each technique is applied to one or more of the following proteins: ferricytochrome c from horse heart and Candida krusei, ferrocytochrome c and cyanoferricytochrome c from horse heart, lysozyme from hen egg white, cyanoferrimyoglobins from horse and sperm whale skeletal muscle, and carbon monoxide myoglobin from horse. In all of the protein spectra we have examined, methine aromatic carbons give rise to broad bands. Studies of the narrow resonances of nonprotonated aromatic carbons of proteins are facilitated by removal of these broad bands by means of the convolution-difference method, preferably from spectra recorded under conditions of noise-modulated off-resonance proton decoupling. We present a summary of the chemical shift ranges for the various types of nonprotonated aromatic carbons of amino acid residues and hemes of diamagnetic proteins, based on our results for hen egg white lysozyme, horse heart ferrocytochrome c, horse carbon monoxide myoglobin, and carbon monoxide hemoglobins from various species...

Animals↗

PubMed1977

Effect of changing the composition of the bathing solutions upon the isometric tension-pCa relationship in bundles of crustacean myofibrils.

1. The relative isometric tension-pCa relationship has been determined for isolated bundles of barnacle myofibrils under a variety of ionic conditions using [Ca(2+)]-buffered solutions which also contained an ATP regenerating system (creatine phosphate and creatine kinase).2. The results are in better agreement with the ;consecutive' scheme of reaction rather than with the ;independent' alternative (Ashley & Moisescu, 1972) for the co-operative action of two Ca(2+) ions in the process of tension activation in crustacean skeletal muscle.3. Variations in the pH of the activating solutions did have a marked effect on the relative tension-Ca curve, although no effect was observed on the absolute maximum value for isometric tension. A shift in pH by 0.5 u. in the range 6.6-7.6 shifted the Ca(2+)-activation curve by 0.5 log u. towards lower free Ca(2+) concentrations.4. Changes in the free Mg(2+) concentration of the activating solutions in the millimolar range produced a pronounced shift of the relative tension-pCa curve along the pCa axis. Increasing [Mg(2+)] from 1 to 5 mM shifted the curve by about 0.7 log u. to higher free Ca(2+) concentrations, without significantly modifying its steepness.5. Changes in the MgATP concentration of the activating solutions in the range of 1-13 mM had no significant effect on the relative tension-pCa relationship.6. Varying the K(+) concentration in the activating solutions was also observed to have a marked effect upon the tension-pCa relationship in barnacle. An increase in the K(+) concentration from 90 to 170 mM shifted the curve by some 0.6 log u. towards higher free Ca(2+) concentrations.7. Cooling the standard activating solutions from room temperature to +4 degrees C made no apparent difference to the relative tension-pCa relationship, but decreased significantly the absolute tension responses.8. The results presented show that tonicity by itself has a marked effect upon the absolute steady-state tension levels in isolated bundles of myofibrils.9. Maximum isometric tension in this preparation was not simply related to ionic strength, or to the monovalent cation concentration, but it depended, as well, upon the anionic composition of the activating solution. In addition, a change in ionic strength of 25 mM over the range of 245-270 mM did not appear to modify the relative tension-pCa relationship.10. The effect of the physiologically occurring cations H(+), K(+), Mg(2+) upon the relative isometric tension-pCa relationship can be accounted for on the basis of a model of competitive inhibition between these cations and Ca(2+) for the functional unit for tension. This inhibitory effect appears to involve at least one H(+), one Mg(2+) and two K(+) per each Ca(2+) ion participating in the activation process of the functional unit for tension.

Adenosine Triphosphate↗

PubMed1977

Direct assignment of the cysteinyl, the slowly exchangeable, and the aromatic ring 1H nuclear magnetic resonances in clostridial-type ferredoxins.

We have directly assigned the 1H NMR corresponding to the cysteinyl protons, the slowly exchangeable protons, and the aromatic ring protons in the 1H NMR spectrum of Clostridium acidi-urici ferredoxin by isotopic labeling and 13C NMR decoupling techniques. We also show that the resonance pattern in the 8- to 20-ppm (from 2,2-dimethyl-2-sialapentanesulfonic acid) region of the 1H NMR spectra of oxidized Clostridium acidi-urici, Clostridium pasteurianum, Clostridium perfringens, and Peptococcus aerogenes ferredoxins are very similar, and we assign the resonances in this region by analogy with the spectrum of C. acidi-urici ferredoxin. The 1H NMR spectra of the beta protons of the cysteinyl residues of these ferredoxins differ, however, from the 1H NMR spectra of equivalent beta protons of the methylene carbon atoms bonded via a sulfur atom to [4Fe-4S] clusters in synthetic inorganic analogues. In the spectra of the synthetic compounds, the beta protons appear as a single resonance shifted 10 ppm from its unbonded reference position. In the spectra of oxidized clostridial ferredoxins, the cysteinyl beta protons appear as a series of at least eight resolved resonances with shifts that range from 6 to 14 ppm, relative to the free amino acid resonance position. This difference in the spectra of the protein and the synthetic compounds probably results from the fact that the equivalent beta protons of the synthetic compounds are not constrained and are free to rotate and thus assume the same average orientation with respect to the [4Fe-4S] cluster. The shift pattern in the 9- to 14-ppm region is identical in three different clostridial ferredoxins. This suggests that the molecular environments of the corresponding cysteinyl residues are identical. Significant differences in the resonance positions occur, however, in the 14- to 18-ppm region, suggesting that the physical environments of these cysteinyl residues differ. This may reflect differences in the orientation of the corresponding cysteinyl residues relative to the [4Fe-4S] clusters or differences in charge density at the cysteinyl beta protons or both. The slowly exchangeable protons were identified by comparing the 1H NMR spectra of ferredoxins reconstituted in H2O and 2H2O. The remaining resonances in the 8- to 20-ppm region were assigned to each of the 2 tyrosyl residues in C. acidi-urici ferredoxin. This was done by comparing the 1H NMR spectra of C. acidi-urici [(3',5'-2H2)Tyr]ferredoxin and C. acidi-urici [PHE2]ferredoxin with that of C. acidi-urici native ferredoxin.

Amino Acids↗

PubMed1977

Epigenetic variation of cultured somatic cells: evidence for gradual changes in the requirement for factors promoting cell division.

Cells of higher plant species in culture sometimes lose their requirement for an exogenous supply of a cell division factor that, thereafter, they are able to produce. This heritable change, known as cytokinin habituation, appears to be an epigenetic one rather than a classical mutation because it is directed, potentially reversible, leaves the cell totipotent, and involves the expression of a latent differentiated function. By using cloned cell lines derived from pith parenchyma of tobacco, we have obtained evidence that the habituation process is gradual rather than all-or-none and leads to progressively more autotrophic tissues. Cells in culture show reversible shifts among a range of habituated states but remain totipotent and can be induced to regain their requirement for a cell division factor. Thus, it appears that habituation involves epigenetic changes in a quantitative cellular phenotype. Our findings support the hypothesis that tumor progression in crown gall, a neoplastic disease of higher plants, can be accounted for by heritable changes in the pattern of gene expression.

Cell Differentiation↗

PubMed1977

Osmotic adaptation to rigid contact lenses.

Using a precision thermocouple hygrometer, requiring just 5 microliters of sample, the tear osmotic pressures of 6 subjects were monitored throughout their adaptation to rigid contact lenses. Relative to the prefitting baselines established for each previous to this study, these subjects showed a range of hypotonic shifts on initially receiving their lenses, but this imbalance was rectified by the end of the first wearing week and a new relatively hypertonic level of tear osmotic pressure was commonly established. This new baseline was reflected in the pre-insertion samples of several of the subjects as well once adaptation was advanced.

Adaptation, Physiological↗

PubMed1979

[Relationship between the minute superslow oscillations and the level of energy supply in brain tissue].

In animals, an increase in glycolysis intensity and processes of oxidative phosphorylation in the brain correlated with the steady potential shifts within the range of 0--1.0 Hz in the neocortex, dorsal hippocampus, and thalamic nuclei. The neurotropic drug ethymizol revealed two effects depending on the initial functional state of the rabbit: 2.5 mg/kg of the drug enhanced the amplitude of the minute waves in the frontal neocortex and dorsal hippocampus, increasing the metabolic rate in the unsteady period of conditioning, whereas after the fast conditioning the drug rendered background values to the minute oscillations and elongated the extinction of conditioned reflexes. The ethymizol appears to be an unspecific connector.

Animals↗

PubMed1979

Carcinogenesis in tissue culture 30: malignant transformation of normal rat liver cells treated with diethylnitrosamine in tissue culture with special reference to the differential effects of cytochalasin B on various cells with and without tumorigenicity.

Liver tissue of a suckling rat was cultured. After 3 weeks of cultivation, the cultures consisting of epithelial cells were treated with 50 micrograms/ml or 100 micrograms/ml DEN for 7 days. 5 months after the treatment, the mode of chromosome number was found decreased from 42 to 40 in the 100 micrograms/ml DEN-treated group and shifted to triploid range after 21 months. The mode in the 50 micrograms/ml DEN-treated group maintained the diploid number until the 5th month but was found reduced to 40 in 21 months. On subcutaneous backtransplantation into young rats at the 22nd month, the treated cells produced tumors at the site inoculated in all the rats. Metastatic foci were also detected in lungs. These tumors were histologically diagnosed as hepatomas. Untreated control cells did not produce tumors. The differential effects of cytochalasine B on the cells with and without tumorigenicity were examined by the use of these cells and other cells, and it revealed that the capacity of multinucleated cell-formation by cytochalasin B fairly corresponds with the backtransplantability of the cells. Binucleated cell formation, not more than 2 nuclei, in the culture of normal cells was found by time-lapse cinemicrography to be not due to the non-capacity of multinucleation but to the destruction of multinucleated cells.

Animals↗

PubMed1976

The action of Ca2+ , Mg2+ and H+ on the contraction threshold of frog skeletal muscle: Evidence for surface charges controlling electro-mechanical coupling.

The dependence of the threshold potential for contraction of pH and the concentration of Ca2+ and Mg2+ in the bathing solution was measured in frog skeletal muscle. Decreasing the pH from 10.3 to 4.65 resulted in a threshold shift to more positive potentials. Between pH 6.5 and 8.5 the concentration threshold was almost pH -independent. Increasing [Ca2+]o (in the concentration range 0.5-50 mM) shifted the curves relating contraction threshold to pH to less negative potentials and diminished the overall pH-dependence. The contraction threshold exhibited a similar dependence on [Ca2+]o and [Mg2+]o, the two curves running parallel in the concentration range of 5-50 mM, but Mg2+ was only c. 0.6 as effective as Ca2+. To explain these results a surface charge model is proposed which assumes that two acidic groups, sigma1 and sigma2, and one basic group, sigma3, reside at the outer surface of the membrane of the T-system. Alterations in the extracellular medium exert their influence on the electro-mechanical coupling process by changing the surface potential. The groups will be titrated by protons and their charges screened off by the divalent cations. In addition, Ca2+ was supposed to bind with a weak dissociation constant (23 M) to the two acidic groups. The chosen charge densities are: sigma1 = -0.0085/A2 [= -1e/(10.8 A)2], sigma2 = -0.0037/A2 [= -1e/(16.4 A)2], sigma3 = 0.0028/A2 [= + 1e/(18.9 A)2] with intrinsic dissociation constants KH1 = 10(-2.0)M, KH2 = 10(-4.1)M, and KH3 = 10(-8.5) M. The measured threshold values are satisfactorily described by this model except at extreme alkaline and acid pH values.

Animals↗

PubMed1979

Covalently bound non-coenzyme phosphorus residues in flavoproteins: 31P nuclear magnetic resonance studies of Azotobacter flavodoxin.

In addition to the 5'-phosphate ester on its flavin mononucleotide (FMN) moiety, flavodoxin from Azotobacter vinelandii contains 2 moles of tightly bound phosphate. One non-coenzyme phosphate group is covalently bound to the protein, as it remains with the protein on acid precipitation, whereas the other phosphate is released. The invariance of the (31)P nuclear magnetic resonance chemical shift of the covalently bound phosphate (-0.8 ppm relative to 85% phosphoric acid) with pH, even in the presence of protein denaturants, implies it is in a diester linkage to the protein. Because no evidence could be found for the presence of covalently bound sugars, nucleotides, or phospholipids, it is suggested that the phosphate residue forms a diester linkage with two hydroxyl amino acids in the protein. The only other suggestion of a phosphodiester linkage in proteins is from previous studies on pepsin and pepsinogen [Perlmann, G. E. (1955) Adv. Prot. Chem. 10, 1-30]. The observed changes in (31)P chemical shift with pH show that the covalent phosphorus in pepsinogen has ionization properties of a monoester rather than a diester. The (31)P resonance of the FMN phosphate occurs at -5.6 ppm in native Azotobacter flavodoxin. No ionization of the protein-bound FMN phosphate is observed since the chemical shift does not change appreciably in the pH range of 5.5-9.5. The chemical shift data suggest, but do not prove, that the coenzyme phosphate in its protein-bound form is dianionic. Chemical analysis of several other flavoenzymes from a variety of sources shows the presence of covalently bound phosphorus in quantities stoichiometric with the flavin content in most of the enzymes tested. Thus, the presence of covalent phosphorus in flavoenzymes may be a general phenomenon with currently unknown catalytic significance.

Apoproteins↗

PubMed2025

Harnessing Landscape Genomics to Evaluate Genomic Vulnerability and Future Climate Resilience in an East Asia Perennial.

In this era of rapid climate change, understanding the adaptive potential of organisms is imperative for buffering biodiversity loss. Genomic forecasting provides invaluable insights into population vulnerability and adaptive potential under diverse climatic conditions, thereby facilitating management interventions and bolstering shaping species-specific germplasm conservation strategies. We primarily employed landscape genomics approaches, leveraging single-nucleotide polymorphisms obtained through whole-genome resequencing of 201 individuals across 43 Rheum palmatum complex populations, to pinpoint adaptive variation and its significance in the context of future climates, delineate seed zones, and establish guidelines for ex situ germplasm conservation. The species complex exhibited strong signatures of local adaptation and differential genomic vulnerabilities across its distribution range, with eastern lineage populations facing significant maladaptation risks under future climate scenarios. Using diverse datasets of putatively adaptive loci and climate change scenarios, we delineated three distinct seed zones within the species' range, estimated varying sample sizes per zone to capture most adaptive diversity, and predicted shifts in seed zone centroids ranging from 48.3 to 359.3 km from historical distributions to mitigate climate change impacts. Collectively, our findings underscore the importance of integrating genomic and environmental data to forecast the adaptive trajectory of an East Asian perennial under anticipated climate changes, guide seed zone delineation for germplasm conservation and enhance population resilience. These results provide a blueprint for designing targeted conservation strategies and restoration plans in other imperilled species.

Climate Change↗

PubMed1979

Very low density and low density lipoprotein subfractions in type III and type IV hyperlipoproteinemia. Chemical and physical properties.

Subfractions of CLDL (VLDL), Sf 100-400; CLDL2, Sf 60--100; VLDL3, Sf 20--60) and LDL (LDL), Sf 12--20; LDL2, Sf 6--12; LDL3, Sf 3--6) were isolated from the plasma of three normal, three type III and four type IV hyperlipoproteinemic subjects. In the type IV group, all VLDL subspecies were of normal composition but were increased in concentration in the order VLDL1 greater than VLDL2 greater than VLDL3. In the same subjects, although LDL2 was lowered and LDL3 increased, the total plasma LDL concentration was normal. All VLDL subfractions were elevated in the type III group, but in this case VLDL3 predominated. These subfractions were enriched in cholesteryl esters and depleted in triglyceride. In the LDL density range there was a shift of mass towards the least dense fraction, LDL1, which was of normal composition. EPR studies of the VLDL and LDL subfractions in a type IV subject demonstrated a decrease in fluidity with increasing density. The major change occurred between VLDL3 and LDL1 and was attributed to a substantial alteration in the cholesteryl ester : triglyceride ratio in the particle. A similar argument was used to explain thction in normal or type IV subjects. Particle diameters, determined by laser light-scattering spectroscopy were in good agreement with the values obtained by electron microscopy. This study provides a baseline for the examination of the relationship between the physical and metabolic properties of VLDL and LDL subfractions in type III and IV hyperlipoproteinemia.

Apolipoproteins↗

PubMed1976

Proton-nuclear-magnetic-resonance study of the conformation of neurotoxin II from Middle-Asian cobra (Naja naja oxiana) venom.

A proton nuclear magnetic resonance (NMR) study at 100 and 300 MHz of neurotoxin II from the venom of Middle-Asian cobra Naja naja oxiana has been performed in 2H2O and H2O solutions. By means of chemical modification and double resonance all the aromatic residue resonances have been assigned. From the NMR titration curves, pK values of histidine 4 and histidine 31 residues have been determined. For one of the two neighbouring tryptophan residues pH dependence (in the 2-8-pH range) of the chemical shifts of indole protons has been revealed. According to the different sensitivity of the linewidth of indole NH resonances to pH in H2O solution, the accessibility of each of the tryptophan residues has been estimated. Temperature dependence has been observed for the linewidth of the aromatic resonances of the tyrosine 24 residue. Deuterium exchange rates have been measured for amide protons as well as for C(2)H histidine resonances. The NMR data obtained have allowed the conclusions to be made that the two histidine residues and one of the tryptophan residues should be localized on the surface of the protein globule, that arginine residues should be present in the environment of histidine 4, that histidine 31 and the buried tryptophan are possibly localized in close spatial proximity and that the side chain of tyrosine 24 is buried within the protein globule.

Amino Acid Sequence↗