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71.
Male voles were reared from birth to age 28 days in 6L:18D. Pairs of animals showing similar sexual development were assigned at random to 16L:8D or 6L:18D. Treatments continued for a further 56 days. Increase in the activity of the hypothalamo-hypophysial system occurred within 4 days of exposure to 16L:8D, as shown by significant elevation of plasma LH and FSH. Pituitary LH did not increase until Day 7, and pituitary FSH did not increase until Day 21. After exposure to 16L:8D for 4 days, pituitary FSH was lower than in corresponding animals in 6L:18D. These discrepancies between pituitary and plasma values of gonadotrophins indicate that increase in hormone release occurs before synthesis is fully stimulated. Enhanced output of testicular hormones probably began between Day 7 and Day 14, as indicated by an increase in seminal vesicle weight, yet plasma and pituitary concentrations of LH and FSH remained elevated. This suggests that long photoperiods may cause direct stimulation of the hypothalamo-hypophysial system which increasing values of testicular hormones are initially unable to inhibit. The response of this system in voles to an abrupt change from a non-stimulating to a stimulating photoperiod has a time course resembling that for the Soay ram but appreciably slower than for the Japanese quail. 相似文献
72.
S Chatterjee K S Clarke P O Kwiterovich 《The Journal of biological chemistry》1986,261(29):13480-13486
The metabolism of low density lipoproteins (LDL), and LDL modified by reductive methylation (M-LDL) of lysine residues, was studied in proximal tubular (PT) cells both from normal human kidney and from urine of patients with homozygous (LDL receptor-negative) familial hypercholesterolemia (FH). LDL and M-LDL was labeled either in the protein moiety with 125I or in the lactosylceramide moiety with 3H. The binding and degradation of 125I-LDL in normal cells was saturable and displaced by unlabeled LDL but not by M-LDL. The uptake of [3H]lactosylceramide (LacCer) low density lipoprotein in normal renal cells was saturable, and time and temperature-dependent. Exogenously derived [3H]LacCer on LDL was rapidly taken up and catabolized to monoglycosylceramide, or it was utilized for the endogenous synthesis of globotriaosylceramide (trihexosylceramide) and globotetraosylceramide (tetraglycosylceramide). [3H]LacCer M-LDL was taken up less avidly and metabolized less extensively than [3H]LacCer-LDL in normal cells. In homozygous FH renal cells the binding of 125I-LDL was not saturable and not displaced by unlabeled LDL. 125I-LDL degradation did not occur in FH cells. The homozygous FH PT cells took up a 2-fold greater amount of exogenously derived [3H]LacCer on LDL than normal cells. Yet, most of the [3H]LacCer taken up by FH PT cells accumulated as LacCer, and only small amounts were metabolized to monoglycosylceramide, globotriaosylceramide (trihexosylceramide), or globotetraosylceramide (tetraglycosylceramide). When normal and FH PT cells were preincubated with LDL (0-100 micrograms/ml medium), there was a 5-fold increase in cellular LacCer levels in FH cells at saturating levels of LDL, whereas there was about a 50% decrease in LacCer levels in normal cells. While the high affinity binding of LDL was not essential for the delivery of LacCer to cells, the data support the conclusion that LDL binding to the LDL receptor facilitates further LacCer processing and metabolism in normal renal cells. We speculate that [3H] LacCer is taken up by FH homozygous cells via a LDL receptor-independent mechanism and accumulates in the cells without significant metabolism. LacCer taken up by this mechanism contributes to the storage of LacCer in FH PT cells. 相似文献
73.
Mammalian protein carboxyl methyltransferases have recently been proposed to recognize atypical configurations of aspartic acid and may possibly function in the metabolism of covalently altered cellular proteins. Consistent with this proposal, the tetrapeptide tetragastrin, containing a single "normal" L-aspartyl residue (L-Trp-L-Met-L-Asp-L-Phe-NH2) was found here not to be an in vitro substrate for erythrocyte carboxyl methyltransferase activity. However, chemical treatment of tetragastrin by methyl esterification and then de-esterification of the aspartic acid residue yielded a mixture of peptide products, the major one of which could now be enzymatically methylated. We show here that this new peptide species is the isomeric beta-aspartyl form of tetragastrin (L-iso-tetragastrin; L-Trp-L-Met-L-Asp-L-Phe-NH2), and it appears that isomerization proceeds via an intramolecular succinimide intermediate during the de-esterification procedure. L-iso-Tetragastrin is stoichiometrically methylated (up to 90% in these experiments) with a Km for the enzyme of 5.0 microM. Similar chemical treatment of several other L-aspartyl peptides also resulted in the formation of new methyltransferase substrates. This general method for converting normal aspartyl peptides to isoaspartyl peptides may have application in the reverse process as well. 相似文献
74.
Transformation of sperm nuclei to metaphase chromosomes in the cytoplasm of maturing oocytes of the mouse 总被引:4,自引:1,他引:3
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Zona-free oocytes of the mouse were inseminated at prometaphase I or metaphase I of meiotic maturation in vitro, and the behavior of the sperm nuclei within the oocyte cytoplasm was examined. If the oocytes were penetrated by up to three sperm, maturation continued during subsequent incubation and became arrested at metaphase II. Meanwhile, each sperm nucleus underwent the following changes. First, the chromatin became slightly dispersed. By 6 h after insemination, this dispersed chromatin had become coalesced into a small mass, from which short chromosomal arms later became projected. Between 12 and 18 h after insemination, each mass of chromatin became resolved into 20 discrete metaphase chromosomes. In contrast, if oocytes were penetrated by four to six sperm, oocyte meiosis was arrested at metaphase I, and each sperm nucleus was transformed into a small mass of chromatin rather than into metaphase chromosomes. If oocytes were penetrated by more than six sperm, the maternal chromosomes became either decondensed or pycnotic, and the sperm nuclei were transformed into larger masses of chromatin. As control experiments, immature and fully mature metaphase II oocytes were inseminated. In the immature oocytes, which were kept immature by exposure to dibutyryl cyclic AMP, no morphological changes in the sperm nucleus were observed. On the other hand, in the fully mature oocytes, which were activated by sperm penetration, the sperm nucleus was transformed into the male pronucleus. Therefore, the cytoplasm of the maturing oocyte develops an activity that can transform the highly condensed chromatin of the sperm into metaphase chromosomes. However, the capacity of an oocyte is limited, such that it can transform a maximum of three sperm nuclei into metaphase chromosomes. Furthermore, the presence of more than six sperm causes a loss of the ability of the oocyte to maintain the maternal chromosomes in a metaphase state. 相似文献
75.
Quantification of arabinogalactan-protein in plant extracts by single radial gel diffusion 总被引:12,自引:0,他引:12
The amount of arabinogalactan-protein in whole plant extracts can be quantified by single radial diffusion in agarose gels containing a dye known as the beta-glucosyl-Yariv reagent which specifically interacts with and precipitates arabinogalactan-proteins. The lower limit of quantification is 0.04 microgram of arabinogalactan-protein; gum arabic is used as a standard reference arabinogalactan-protein. In principle, this method can be adapted to measure levels of any dye-precipitating macromolecule; for example, acidic polysaccharides can be estimated by their binding to the cationic dye Alcian blue. 相似文献
76.
Seasonal changes in LH secretion in normal ewes and ewes which grazed oestrogenic clover 总被引:1,自引:0,他引:1
Plasma luteinizing hormone (LH) concentrations were measured in normal (control) Corriedale X Merino (comeback) ewes and in clover-infertile comeback ewes which had grazed oestrogenic Yarloop clover (Trifolium subterraneum L. cv. Yarloop) for more than 4 years. Plasma LH concentrations were measured in samples taken at 20-min intervals for 6 h during the dioestrous stage of the oestrous cycle in the breeding season (BS) and during the anoestrous season (AS). In the control ewes during BS, transitory elevation in plasma LH concentration (pulses) occurred, reflecting secretory episodes, with a frequency of one per 5.2 h. This frequency fell to one per 16.5 h during the anoestrous season. In clover-infertile ewes, LH pulses occurred with a frequency of one per 4.5 h during BS and one per 4.9 h during AS (difference not significant). In the controls, plasma LH levels were higher (P less than 0.05) during BS (mean +/- s.d. = 1.2 +/- 0.4 ng/ml, n = 9) than in AS (0.7 +/- 0.3 ng/ml, n = 5). In the clover-infertile ewes, plasma LH levels in BS (1.3 +/- 0.6 ng/ml, n = 12) were similar to those of controls. During AS, plasma LH levels in the clover-infertile ewes (1.0 +/- 0.6 ng/ml, n = 10) remained similar to their BS levels, being significantly (P less than 0.05) higher than LH levels in the controls at this time. These studies indicate that the higher plasma concentrations of LH which have been reported in clover-infertile ewes arise from more frequent LH pulses. Furthermore, in contrast to normal ewes, average plasma LH, reflecting pulse frequency, is not reduced in AS. This supports the view that ingestion of phytooestrogens affects neural centres involved in regulating LH secretion. 相似文献
77.
Inhibition of protein carboxyl methylation by S-adenosyl-L-homocysteine in intact erythrocytes. Physiological consequences 总被引:4,自引:0,他引:4
S-Adenosyl-L-homocysteine was used to inhibit the methylation of carboxylic acid residues of membrane proteins in intact human erythrocytes. Incubation of erythrocytes for 24 h with 5 mM each of adenosine and L-homocysteine resulted in the intracellular accumulation of S-adenosyl-L-homocysteine and substantially inhibited membrane protein carboxyl methylation. From the degree of inhibition and from the observed turnover of methylated proteins, we estimate that the number of protein methyl esters in cells incubated with adenosine and L-homocysteine for 20 h is less than 20% that of cells incubated without these inhibitors. No significant differences in the physical deformability properties of the membrane of these hypomethylated cells were detected. However, there was a small but significant (p less than 0.001) increase in the amount of membrane protein D-aspartyl residues in these cells compared to control cells. These observations are consistent with the hypothesis that methylation of membrane proteins at D-aspartyl residues may result in the selective removal or repair of these uncommon residues. 相似文献
78.
A limited region within hen egg-white lysozyme serves as the focus for a diversity of T cell clones 总被引:11,自引:0,他引:11
F Manca J A Clarke A Miller E E Sercarz N Shastri 《Journal of immunology (Baltimore, Md. : 1950)》1984,133(4):2075-2078
The C57BL/6 (H-2b) mouse is a nonresponder to hen egg-white lysozyme (HEL) injected i.p., owing to a T suppressor cell-inducing determinant at the amino-terminal region. After immunization with a 93-amino acid fragment (a.a. 13-105) of HEL lacking this determinant, all clones from two independently derived C57BL/6 T cell lines were found to be specific for epitopes within a subregion of peptide 74-96. Three specificity patterns for the clones could be defined on the basis of cross-reactivities with only two other species variant lysozymes. Reactivities of all three specificity groups was consistent with the serine to threonine substitution at position 91, although reactivity of one of the groups could be affected by substitutions at position 84. The results confirm at the clonal level that even for distantly related antigens, only limited regions are recognized by T cells. They are consistent with the notion that specific sites on the antigen capable of interaction with Ia molecules lead to dominance of certain regions for T cell reactivity. Moreover, the diversity in specificity among clones suggests that the limiting feature of T cell responsiveness is not a lack of available T cells in the repertoire directed against a single antigenic site. 相似文献
79.
S H Clarke J J Kenny D G Sieckmann S Rudikoff 《Journal of immunology (Baltimore, Md. : 1950)》1984,132(3):1544-1549
Mice expressing the xid gene exhibit an altered immune response to phosphocholine (PC)-conjugated keyhole limpet hemocyanin (KLH). Less than 25% of their anti-PC-KLH response is PC specific, and most of these antibodies lack the normally predominant T15 idiotype. These findings suggested that immune defective mice might employ different variable region genes than normal mice in their anti-PC response. To examine this possibility, we characterized by Southern blot analysis the gene family encoding PC-VH regions and determined the amino acid sequence and fine specificity of binding of a T15-, IgG2, PC-specific hybridoma (1B8E5) produced by fusion of the SP2/O cell line and PC-KLH immune CBA/N spleen cells. Southern blot analysis of DNA from CBA/N mice by using a PC-VH probe (S107 VH) revealed a hybridization pattern virtually identical to that of DNA from normal CBA/J mice, indicating that CBA/N mice do not suffer from a gross deletion of PC-VH genes. Analysis of the 1B8E5 antibody reveals that both the binding specificity and relative affinity of this antibody are different from the anti-PC antibodies of the T15, M167-M511, and M603 families. The complete amino acid sequence of the heavy (H) chain variable region shows that 1B8E5 uses a VH segment identical to the allelic form of T15 (C3) but has a unique D region of three amino acids and use the JH1 joining segment. Both the DH and JH regions are unusual when compared to PC-specific antibodies from normal mice, which have a D region composed of five to eight amino acids and use the JH1 joining segment. The amino terminal sequence of the 1B8E5 light (L) chain demonstrates that this anti-PC antibody carries a Vk3 subgroup L chain. Chains from this subgroup have not previously been found in association with PC-binding antibodies. Thus, the Vk, DH, and JH segments expressed in 1B8E5 make this hybridoma unique in terms of the anti-PC antibodies studied to date, and suggests that additional PC-specific antibodies exist in inbred mice that employ "unusual" V gene segments. 相似文献
80.
Vaccination against schistosomiasis in mice with killed schistosomula without adjuvant 总被引:1,自引:0,他引:1
S Y Hsü H F Hsü K W Svestka W Clarke 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1986,181(3):454-458
Attempts to develop a killed vaccine against schistosomiasis have generally resulted in failure. There are two recent reports, but unfortunately, harsh adjuvants were used in conjunction with the antigenic materials. In our laboratory, a killed vaccine was developed by freezing (-196 degrees C) and thawing the schistosomula of S. mansoni. The use of such a preparation without adjuvant was effective in vaccinating mice. A worm reduction of 36.4-41.1% was achieved by one vaccinating injection, a 60.2% worm reduction by 3 injections, and a 63.7-66.0% reduction by 5 injections. The sequence of the development and the expression of the immune reactions were similar to those previously found in hosts immunized with highly X-irradiated schistosome organisms. Delayed hypersensitivity was demonstrated in histological sections of the skin in the challenged mice after one vaccination, showing that an adjuvant was not necessary to initiate the induction of cellular immunity. 相似文献