The effect of extracellular ice and cryoprotective agents on the water permeability parameters of human sperm plasma membrane during freezing.
(73/2521)
A firm biophysical basis for the cryopreservation of human spermatozoa is limited by a lack of knowledge regarding the water permeability characteristics during freezing in the presence of extracellular ice and cryoprotective agents (CPA). Cryomicroscopy cannot be used to measure dehydration during freezing in human spermatozoa because of their highly non-spherical shape and their small dimensions which are at the limits of light microscopic resolution. Using a new shape-independent differential scanning calorimeter (DSC) technique, volumetric shrinkage during freezing of human sperm cell suspensions was obtained at cooling rates of 5 and 10 degrees C/min in the presence of extracellular ice and CPA. Using previously published data, the human sperm cell was modelled as a cylinder of length 40.2 micrometer and a radius of 0.42 micrometer with an osmotically inactive cell volume, V(b), of 0.23V(o), where V(o) is the isotonic cell volume. By fitting a model of water transport to the experimentally obtained volumetric shrinkage data, the best fit membrane permeability parameters (L(pg) and E(Lp)) were determined. The 'combined best fit' membrane permeability parameters at 5 and 10 degrees C/min for human sperm cells in modified media are: L(pg) = 2. 4x10(-14) m(3)/Ns (0.14 micrometer/min-atm) and E(Lp) = 357.7 kJ/mol (85. 5 kcal/mol) (R(2) = 0.98), and in CPA media (with 6% glycerol and 10% egg yolk) are L(pg)[cpa] = 0.67x10(-14) m(3)/Ns (0.04 micrometer/min-atm) and E(Lp)[cpa] = 138.9 kJ/mol (33.2 kcal/mol) (R(2) = 0.98). These parameters are significantly different from previously published parameters for human spermatozoa obtained at suprazero temperatures and at subzero temperatures in the absence of extracellular ice. The parameters obtained in this study also suggest that damaging intracellular ice formation (IIF) could occur in human sperm cells at cooling rates as low as 25-45 degrees C/min, depending on the concentrations of the CPA. This may help to explain the discrepancy between the empirically determined optimal cryopreservation cooling rates (<100 degrees C/min) and the numerically predicted optimal cooling rates (>7000 degrees C/min) obtained using previously published suprazero human sperm permeability parameters which do not account for the presence of extracellular ice. (+info)
Characterization of tBid-induced cytochrome c release from mitochondria and liposomes.
(74/2521)
tBid, the cleaved form of Bid, can induce cytochrome c (Cyt. c) release from rat heart mitochondria more efficiently and reproducibly than that from liver or brain mitochondria. Unlike Bax, such release was not prevented by cyclosphorin A, an inhibitor of the opening of permeability transition pore. Carbonyl-cyanide m-chlorophenyl-hydrazone or oligomycin also have no obvious effect on the release of Cyt. c. In contrast to ceramide, tBid-mediated Cyt. c release from mitochondria is independent of the redox state of Cyt. c. Furthermore, Bid or tBid can directly trigger the efflux of encapsulated Cyt. c or trypsin within liposomes without involvement of other protein factors. (+info)
Thermal tolerance, climatic variability and latitude.
(75/2521)
The greater latitudinal extents of occurrence of species towards higher latitudes has been attributed to the broadening of physiological tolerances with latitude as a result of increases in climatic variation. While there is some support for such patterns in climate, the physiological tolerances of species across large latitudinal gradients have seldom been assessed. Here we report findings for insects based on published upper and lower lethal temperature data. The upper thermal limits show little geographical variation. In contrast, the lower bounds of supercooling points and lower lethal temperatures do indeed decline with latitude. However, this is not the case for the upper bounds, leading to an increase in the variation in lower lethal limits with latitude. These results provide some support for the physiological tolerance assumption associated with Rapoport's rule, but highlight the need for coupled data on species tolerances and range size. (+info)
Comparison of the solution conformation and dynamics of antifreeze glycoproteins from Antarctic fish.
(76/2521)
The (1)H- and (13)C-NMR spectra of antifreeze glycoprotein fractions 1-5 from Antarctic cod have been assigned, and the dynamics have been measured using (13)C relaxation at two temperatures. The chemical shifts and absence of non-sequential (1)H-(1)H NOEs are inconsistent with a folded, compact structure. (13)C relaxation measurements show that the protein has no significant long-range order, and that the local correlation times are adequately described by a random coil model. Hydroxyl protons of the sugar residues were observed at low temperature, and the presence of exchange-mediated ROEs to the sugar indicate extensive hydration. The conformational properties of AFGP1-5 are compared with those of the previously examined 14-mer analog AFGP8, which contains proline residues in place of some alanine residues (Lane, A. N., L. M. Hays, R. E. Feeney, L. M. Crowe, and J. H. Crowe. 1998. Protein Sci. 7:1555-1563). The infrared (IR) spectra of AFGP8 and AFGP1-5 in the amide I region are quite different. The presence of a wide distribution of backbone torsion angles in AFGP1-5 leads to a rich spectrum of frequencies in the IR spectrum, as interconversion among conformational states is slow on the IR frequency time scale. However, these transitions are fast on the NMR chemical shift time scales. The restricted motions for AFGP8 may imply a narrower distribution of possible o, psi angles, as is observed in the IR spectrum. This has significance for attempts to quantify secondary structures of proteins by IR in the presence of extensive loops. (+info)
Ovulation side and cycle fecundity: a retrospective analysis of frozen/thawed embryo transfer cycles.
(77/2521)
The aim of the study was to evaluate a possible lateral difference in ovarian activity and its effect on cycle fecundity. A database was analysed retrospectively which covered 477 cycles in which frozen/thawed embryo transfer had been carried out. The cycles were spontaneous, with no hormonal treatment. Women with ovulation problems as a reason for infertility treatment were excluded. Factors investigated were the side of ovulation, endometrial thickness on cycle days 10-12 and on the day of embryo transfer, and pregnancy rate per embryo transfer. Ovulation was right-sided in 273 of the 477 cycles (57.2%) and left-sided in 204 of the cycles (42. 8%) (95% CI 38.3-47.2, P = 0.002). In the age category of 30-37 years, covering 288 cycles, the incidence of left-sided ovulation was 126 (43.7%, 95% CI 38.0-49.5, P = 0.034). In this category, the endometrial thickness (+/-SD) was significantly greater on the day of embryo transfer (i.e. at time of implantation) when there had been left-sided ovulation compared with right-sided [9.6 mm (2.0) versus 9.1 mm (1.8), P = 0.037]. In addition, the pregnancy rate per embryo transfer was higher when ovulation had been on the left side [32/126 (25.2%) versus right side 24/162 (14.8%), P = 0.035, 95% CI 0.0122-0.199]. In conclusion, right-sided ovulation was more frequent than left-sided in the whole group. This is the first study to report that the side of ovulation has a clinical impact. These data support the hypothesis that the side of ovulation is significant in terms of embryo implantation. (+info)
EPR study of the dinuclear active copper site of tyrosinase from Streptomyces antibioticus.
(78/2521)
The [Cu(I)-Cu(II)] half-met form of the dinuclear copper site of tyrosinase has been probed by continuous wave electron paramagnetic resonance (EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopy in the presence and absence of inhibitors. In all cases the EPR spectrum is indicative of a d(x(2)-y(2)) ground state for the unpaired electron. From the cross-peaks observed in the HYSCORE spectra, proton hyperfine coupling constants were obtained that are compatible with a hydroxide ion in an equatorial coordination position of the paramagnetic copper. After changing the water solvent to D(2)O or after addition of the inhibitors p-nitrophenol or L-mimosine, the proton signals disappear. The relevance of these findings for understanding the catalytic cycle is discussed. (+info)
Annexin II is associated with mRNAs which may constitute a distinct subpopulation.
(79/2521)
Protein-mRNA interactions affect mRNA transport, anchorage, stability and translatability in the cytoplasm. During the purification of three subpopulations of polysomes, it was observed that a 36-kDa protein, identified as annexin II, is associated with only one specific population of polysomes, namely cytoskeleton-associated polysomes. This association appears to be calcium-dependent since it was sensitive to EGTA and could be reconstituted in vitro. UV irradiation resulted in partial, EGTA-resistant cross-linking of annexin II to the polysomes. Binding of (32)P-labelled total RNA to proteins isolated from the cytoskeleton-bound polysomes on a NorthWestern blot resulted in a radioactive band having the same mobility as annexin II and, most importantly, purified native annexin II immobilized on nitrocellulose specifically binds mRNA. The mRNA population isolated from cytoskeleton-bound polysomes binds to annexin II with the highest affinity as compared with those isolated from free or membrane-bound polysomes. Interestingly, the annexin II complex, isolated from porcine small intestinal microvilli was a far better substrate for mRNA binding than the complex derived from transformed Krebs II ascites cells. When cytoskeleton-associated polysomes were split into 60 S and 40 S ribosomal subunits, and a peak containing mRNA complexes, annexin II fractionated with the mRNAs. Finally, using affinity purification of mRNA on poly(A)(+)-coupled magnetic beads, annexin II was only detected in association with messenger ribonucleoproteins (mRNPs) present in the cytoskeletal fraction (non-polysomal mRNPs). These results, derived from both in vitro experiments and cell fractionation, suggest that annexin II binds directly to the RNA moiety of mRNP complexes containing a specific population of mRNAs. (+info)
The use of cryopreserved lymphocytes for longitudinal studies of immune function and enumeration of subpopulations.
(80/2521)
The responses of fresh and frozen lymphocytes to mitogens and antigens have been compared using samples collected on five separate occasions from one normal donor. The day-to-day variation seen with the fresh cells was eliminated by the use of frozen cells. Thawed cells from one donor collected on one occasion but studied on five separate occasions and compared to fresh cells on the same days, showed fluctuations from day to day as well, confirming that the day-to-day variation seen is due to technical and not biological phenomena. Cryopreserved cells showed a decrease in responses to specific microbial antigens, a slight shift in the PHA dose-response curve, but no significant difference in responses to Con A or PWM. The relative proportion of lymphocyte subpopulations changed with freezing and thawing. The proportion of T cells increased slightly and the proportion of B cells decreased. (+info)