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排序方式: 共有96条查询结果,搜索用时 15 毫秒
1.
J M Suttie D L Foster B A Veenvliet T R Manley I D Corson 《Journal of reproduction and fertility》1991,92(1):33-39
The effect of maintaining female sheep at a body weight intermediate between the normal weight for puberty (30-35 kg) and 20 kg (puberty suppressed) on the onset of oestrous cycles was studied. In addition, the influence of ad-libitum food intake or insulin infusion was studied in animals previously maintained at 20 kg. Coopworth ewe lambs (10 weeks old) were allocated to one of 6 treatments: (A) ad-libitum fed (n = 6), (B) ad-libitum fed to 28 kg then maintained at that weight (n = 6), (C) ad-libitum fed to 24 kg then maintained at that weight (n = 6), (D) maintained at 20 kg until Week 29 and then fed ad libitum (n = 6), (E) maintained at 20 kg and infused with 0.1 U insulin/kg/24 h for 2 weeks from 29-31 weeks of age (n = 5), (F) maintained at 20 kg (n = 6). The lambs were penned indoors under natural photo-period, which was decreasing virtually throughout the study, and fed a pelleted concentrate diet which was recorded daily. They were blood sampled twice a week, and plasma was analysed for progesterone. Puberty was defined as the date when plasma concentrations of progesterone first exceeded 1 ng/ml. In addition, ewes in Groups D, E and F were blood sampled every 10 min for 8 h on Days 0 and +12 of the insulin infusion or access to ad-libitum feeding and the plasma was analysed for luteinizing hormone (LH).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
2.
The microenvironments of the histidines in three isoforms of Ca(II)-bound parvalbumin (carp, pI = 4.25; pike, pI = 5.00; rat, pI = 5.50) have been examined with 1H NMR techniques to probe their protonation characteristics and photochemically induced dynamic nuclear polarizability (photo-CIDNP). The histidine at position 26 (or 25), present in all three of these proteins, shows absolutely no photo-CIDNP enhancement of its C2H or C5H resonances. Nor does this nonpolarizable histidine possess a normal pKa: values range only from 4.20 for carp to 4.32 for pike to 4.44 for rat. The C2H and C5H resonances of the histidine in this carp isoform split into doublets as the pH is lowered. The magnitude of this splitting depends on the magnetic field strength, temperature, and pH; however, the line intensities within each doublet are temperature-independent. Although the crystal structure of carp parvalbumin indicates that His-26 is exposed to solvent [Kretsinger, R. H., & Nockolds, C. E. (1973) J. Biol. Chem. 248, 3313-3326], we conclude that in solution this residue, in its unprotonated state, is part of the hydrophobic core of the protein. In contrast, His-48 in rat parvalbumin and His-106 in pike III parvalbumin show dramatic photo-CIDNP enhancements of their C2H, C5H, and beta-CH2 1H NMR resonances. Combined with its nearly normal pKa, 6.14, and exchange-broadened C2H resonance, the photo-CIDNP enhancement results for His-48 indicate that its microenvironment differs little from random-coil exposure, consistent with its presumed position on the solvent surface of helix C.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
3.
Lacking the extraordinary thermal stability of its metal-bound forms, apo-alpha-parvalbumin from rat muscle assumes two distinct conformations in aqueous solution. At 25 degrees C, its highly structured form predominates (Keq = 5.7; delta G degree = -4.3 kJ X mol-1); as deduced from both 1H NMR and circular dichroism (CD) spectroscopy, this conformation is exceedingly similar to those of its Mg(II)-, Ca(II)-, and Lu(III)-bound forms. The temperature dependences of several well-resolved aromatic and upfield-shifted methyl 1H NMR resonances and several CD bands indicate that the native, highly helical structure of rat apo-alpha-parvalbumin is unfolded by a concerted mechanism, showing no indication of partially structured intermediates. The melting temperature, TM, of rat apo-alpha-parvalbumin is 35 +/- 0.5 degrees C as calculated by both spectroscopic techniques. By 45 degrees C, rat apo-alpha-parvalbumin unfolds entirely, losing the tertiary structure that characterizes its folded form: not only are the ring-current-shifted aromatic and methyl 1H NMR resonances leveled, but the 262- and 269-nm CD bands are also severely reduced. As judged by the decrease in the negative ellipticity of the 222-nm CD band, this less-structured form of rat apo-alpha-parvalbumin shows an approximate 50% loss in apparent alpha-helical content compared to its folded state. Several changes in the 1H NMR spectrum of rat apo-alpha-parvalbumin were exceptionally informative probes of the specific conformational changes that accompany metal ion binding and metal ion exchange. In particular, the line intensities of the ortho proton resonance of Phe-47, the unassigned downfield-shifted alpha-CH resonances from the beta-sheet contacts between the metal-binding loops, the C2H resonance of His-48, and the epsilon-CH3 resonance of an unassigned Met residue were monitored as a function of added metal to determine the stability constants of several metal ion-parvalbumin complexes. We conclude that Mg(II) binds to the CD and EF sites independently, its affinity for the EF site being almost twice that for the CD site. Mg(II)----Ca(II) exchange showed that the CD-site Mg(II) is displaced first, in contrast to Lu(III)'s preferential displacement of the EF-site Ca(II) as determined from the Ca(II)----Lu(III) exchange experiments.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
4.
Optical stopped-flow techniques have been used to determine the dissociation rate constants (koff) for the lanthanide(III) ions from carp (pI 4.25) parvalbumin. For most of the 13 different lanthanides studied, the release kinetics were diphasic, composed of both a fast phase (whose rate varied across the series, La3+ leads to Lu3+, between the limits -1.2 less than or equal to log kFAST less than or equal to -0.7) and a slower phase (whose rate varied across the series, La3+ leads to Lu3+, between the limits -1.2 greater than or equal to log kSLOW greater than or equal to -2.9). In addition, the La3+- and Lu3+-induced changes in the 270-MHz proton nuclear magnetic resonance spectrum of parvalbumin were used to calculate the dissociation constants for these specific lanthanides from the two high-affinity Ca2+ binding sites. The KD for one site appears to remain constant across the lanthanide series, determined to be 4.8 X 10(-11) M for both La3+ and Lu3+. The other site, however, is evidently quite sensitive to the nature of the bound Ln3+ ion and shows a strong preference for La3+ (KD,La = 2.0 X 10(-11) M; KD,Lu = 3.6 X 10(-10) M). We conclude from these observations that reports of nearly indistinguishable CD/EF binding site affinities for parvalbumin complexes of the middle-weight lanthanides (i.e., Eu3+, Gd3+, and Tb3+) are quite reasonable in view of the crossover in relative CD/EF site affinities across the lanthanide series. 相似文献
5.
George E. Corson Jr. 《American journal of botany》1969,56(10):1127-1134
Seedlings of Datura stramonium L., although not photoperiodically sensitive, are useful for floral transition studies when raised in a growth chamber at a constant temperature of 25 C with a photoperiod of 8 hr of light (1,600-2,000 ft-c) and 16 hr of darkness. A terminal flower is formed after the seventh or eighth leaf primordium is produced. A constant rate of leaf initiation up to the time of flowering enables specific apical stages to be obtained and studied. Changes in the mitotic index, substantiated with calculated rates of cell division (measured by the accumulation of metaphases following treatment with colchicine) were studied in shoot apical zones during transition to flowering. Fluctuations in the mitotic index of each zone in the vegetative and transition apex with respect to apical stage as well as time of day were not statistically significant. The mitotic index of the summit zone of the vegetative apex was significantly lower than in the other zones whose mitotic indices were not significantly different from one another. During floral transition the mitotic index of the summit zone as well as the central zone (just below the summit zone) significantly increased while no significant changes were detected in the flank zones. It was shown that the mitotic index could be considered representative of the rates of cell division in Datura. 相似文献
6.
L F Golden D C Corson B D Sykes D Banville J P MacManus 《The Journal of biological chemistry》1989,264(34):20314-20319
High resolution 1H nuclear magnetic resonance spectroscopy and optical stopped-flow techniques have been used to study the metal binding properties of a site-specific mutant of bacterial recombinant oncomodulin in which glutamate has replaced a liganding aspartate at position 59 in the CD calcium-binding site. In particular we have followed the replacement of calcium by lutetium in bacterial recombinant oncomodulin and D59E oncomodulin to provide a measure of the protein's preferences for metal ions of different ionic radii. The result of the Asp----Glu substitution is to make the mutant oncomodulin more similar to rat parvalbumin in terms of its relative CD- and EF-domain affinities for lutetium(III), that is to increase its affinity for metal ions with smaller ionic radii. This finding supports the original hypothesis that the presence of Asp at sequence position 59 is an important factor in the reduced preference of the CD site of oncomodulin for smaller metals such as magnesium (Williams, T. C., Corson, D. C., Sykes, B. D., and MacManus, J. P. (1987) J. Biol. Chem. 262, 6248-6256). However, our studies show that both the CD and the EF sites are affected by this single residue substitution suggesting that many factors play a role in the metal binding affinity and interaction between the two sites. 相似文献
7.
Angiotensin II stimulates the pp44 and pp42 mitogen-activated protein kinases in cultured rat aortic smooth muscle cells. 总被引:5,自引:0,他引:5
J L Duff B C Berk M A Corson 《Biochemical and biophysical research communications》1992,188(1):257-264
Vasoconstrictors such as angiotensin II (ang II) stimulate vascular smooth muscle cell growth and share many signal transduction mechanisms with growth factors. Recently, growth factors have been shown to stimulate mitogen-activated protein (MAP) kinases, a family of serine/threonine protein kinases which phosphorylate pp90rsk, a cytosolic kinase that phosphorylates ribosomal S6 protein. We examined the effect of ang II on MAP kinase activity and phosphorylation. Ang II stimulated MAP kinase activity by 4-fold after 5 min exposure and also increased tyrosine phosphorylation of 42 kDa (74 +/- 41%) and 44 kDa (263 +/- 85%) proteins, shown to be pp42mapk and pp44mapk by Western blot analysis using a MAP kinase antibody. These results suggest that ang II-stimulated protein synthesis is mediated by a MAP kinase dependent pathway. 相似文献
8.
9.
Studies of hepatitis C virus (HCV) infection amongst injecting drug users (IDUs) have suggested that this population can be separated into two risk groups (naive and experienced) with different injecting risk behaviours. Understanding the differences between these two groups and how they interact could lead to a better allocation of prevention measures designed to reduce the burden of HCV in this population. In this paper we develop a deterministic, compartmental mathematical model for the spread of HCV in an IDU population that has been separated into two groups (naive and experienced) by time since onset of injection. We will first describe the model. After deriving the system of governing equations, we will examine the basic reproductive number $R_0$ , the existence and uniqueness of equilibrium solutions and the global stability of the disease free equilibrium (DFE) solution. The model behaviour is determined by the basic reproductive number, with $R_0=1$ a critical threshold for endemic HCV prevalence. We will show that when $R_0\le 1$ , and HCV is initially present in the population, the system will tend towards the globally asymptotically stable DFE where HCV has been eliminated from the population. We also show that when $R_0>1$ there exists a unique non-zero equilibrium solution. Then we estimate the value of $R_0$ from epidemiological data for Glasgow and verify our theoretical results using simulations with realistic parameter values. The numerical results suggest that if $R_0>1$ and the disease is initially present then the system will tend to the unique endemic equilibrium. 相似文献
10.