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71.
J C Brochon P Wahl M Charlier J C Maurizot C Hélène 《Biochemical and biophysical research communications》1977,79(4):1261-1271
A new crystal form of a mitogenic lectin from pea seeds () has been obtained which is suitable for high resolution structural work. The crystals are orthorhombic, space group P212121, with unit cell dimensions: = 64.2Å, = 72. 7Å, = 108. 3Å. The asymmetric unit contains one protein molecule. 相似文献
72.
73.
74.
J Martal M C Lacroix C Loudes M Saunier S Wintenberger-Torrès 《Journal of reproduction and fertility》1979,56(1):63-73
Trophoblastin, an antiluteolytic component from the embryo, was identified in the ewe by the means of intrauterine injections of homogenates from trophoblasts at 14--16 days pregnancy. Homogenates from embryos and their membranes at 21--23 days pregnancy did not extend the life of the corpus luteum, suggesting that trophoblastin synthesis occurs for only a short period. The trophoblastin was thermolabile (80 degrees C for 30 min) and inactivated by pronase. Treatment of ewes with oCS, hCG, and extracts of 120-day placentae did not affect the time of luteolysis. The protein appears to be insoluble at pH 7 or 8, but to dissolve readily at pH 9.6. After injection of homogenates or extracts from 15--16-day-old trophoblasts, the initial CL were maintained for more than 1 month in most cyclic recipient ewes. Surgical removal of embryos at 21--23 days resulted in luteal maintenace for more than 1 month in over 50% of the operated animals. All the maintained CL were secretory although their average weight was about one-half of that CL of normal pregnancy, suggesting the existence of complementary luteotrophic placental factors. The uteri of most of these pseudopregnant ewes were distended with a clear, sterile fluid. 相似文献
75.
76.
Phenotypic exclusion in mouse melanoma-rat hepatoma hybrid cells: pigment and albumin production are not reexpressed simultaneously. 总被引:11,自引:0,他引:11
Hybridization of cells of defined and different histotypes has been carried out to investigate whether the expression (or reexpression) of parental functions is mutually exclusive, as is expected if the generally assumed rule of discreteness of differentiation applies to hybrid cells. A cross of pigmented mouse melanoma cells and albumin-producing rat hepatoma cells gave rise to hybrids containing essentially one set of chromosomes from each parent and producing neither melanin nor albumin. Cells of one hybrid clone are shown to retain the potential to reexpress both parental differentiations. Successive subclonings of this hybrid have shown that cells which reexpress one function may retain the potential to reexpress the other, and that freshly isolated, morphologically homogeneous subclones may produce pigment or albumin, but not both; there successive and exclusive shifts of phenotype are documented, and in these cases, chromosome loss is very slight. The use of immunoadsorbed antisera has revealed that most (if not all) of the albumin produced by the hybrid cells is of the mouse type. We conclude that both parental determinations are retained by the hybrid cells, and that the parental differentiations are reexpressed only in a mutually exclusive fashion. 相似文献
77.
78.
Surveys dealing with enzyme polymorphisms have recently been conducted in the Sahara. Results from two populations are reported here: 227 inhabitants of Ideles village (Ahaggar, Algeria); 285 nomads of a genetic isolate, the Kel Kummer Twareg tribe (Menaka, Mali). The four classical molecular variants of G6PD:A+, A-, B+, B-, are found in Ideles. The frequency of the G6PD A+ Negroid variant reaches 15% in Ideles and 7.7% among the Kel Kummer. However, gene frequencies will have to be recalculated after a study of the genetic transmission through families. The PGDC gene of 6PGD is especially frequent in the Kel Kummer where 10 'Canning' phenotypes have been observed. The PGM distribution of alleles at locus 1 in Ideles is the same as in the Mediterranean populations. The pa gene of acid phosphatase, relatively frequent in Ideles, has been excluded by drift from the Kel Kummer gene pool. AK and LDH enzymes have also been studied in both samples. The abnormal Ea1 mutation of serum pseudocholinesterase exists in Ideles and in the Kel Kummer as in other populations of the Sahara; the C5 esterase component was revealed by electrophoresis in 5% of the Kel Kummer people. 相似文献
79.
N Gironès E Alverez A Seth I M Lin D A Latour R J Davis 《The Journal of biological chemistry》1991,266(28):19006-19012
It has been reported that the sequence Tyr20-X-Arg-Phe23 present within the cytoplasmic tail of the transferrin receptor may represent a tyrosine internalization signal (Collawn, J.F., Stangel, M., Kuhn, L.A., Esekogwu, V., Jing, S., Trowbridge, I.S., and Tainer, J. A. (1990) Cell 63, 1061-1072). However, as Tyr20 is not conserved between species (Alvarez, E., Gironès, N., and Davis, R. J. (1990) Biochem. J. 267, 31-35), the functional role of the putative tyrosine internalization signal is not clear. To address this question, we constructed a series of 32 deletions and point mutations within the cytoplasmic tail of the human transferrin receptor. The effect of these mutations on the apparent first order rate constant for receptor endocytosis was examined. It was found that the region of the cytoplasmic tail that is proximal to the transmembrane domain (residues 28-58) is dispensable for rapid endocytosis. In contrast, the distal region of the cytoplasmic tail (residues 1-27) was found to be both necessary and sufficient for the rapid internalization of the transferrin receptor. The region identified includes Tyr20-X-Arg-Phe23, but is significantly larger than this tetrapeptide. It is therefore likely that structural information in addition to the proposed tyrosine internalization signal is required for endocytosis. To test this hypothesis, we investigated whether a heterologous tyrosine internalization signal (from the low density lipoprotein receptor) could function to cause the rapid endocytosis of the transferrin receptor. It was observed that this heterologous tyrosine internalization signal did not allow rapid endocytosis. We conclude that the putative tyrosine internalization signal (Tyr20-Thr-Arg-Phe23) is not sufficient to determine rapid endocytosis of the transferrin receptor. The data reported here indicate that the transferrin receptor internalization signal is formed by a larger cytoplasmic tail structure located at the amino terminus of the receptor. 相似文献
80.
F Chirat A Martinage G Briand M Kouach A Van Dorsselaer M Loir P Sautière 《European journal of biochemistry》1991,198(1):13-20
The ram transition protein 1 (TP1) is present in spermatid cell nuclei in the nonphosphorylated, monophosphorylated and diphosphorylated forms. Its primary structure was determined by automated Edman degradation of S-carboxamidomethylated protein and of peptides generated by cleavage with thermolysin and endoproteinase Lys-C. The ram TP1 is a small basic protein of 54 residues and structurally very close to other mammalian TP1. The mass spectrometric data obtained from the protein and its fragments reveal that ram TP1 is indeed a mixture (approximately 5:1) of two structural variants (Mr 6346 and 6300). These variants differ only by the nature of the residue at position 27 (Cys in the major variant and Gly in the minor variant). The study of phosphorylation sites has shown that four different serine residues could be phosphorylated in the monophosphorylated TP1, at positions 8, 35, 36 or 39. From previous physical studies, it has been postulated that the Tyr32 surrounded by two highly conserved basic clusters was responsible for the destabilization of chromatin by intercalation of its phenol ring between the bases of double-stranded DNA. The presence of three phosphorylatable serine residues in the very conserved sequence 29-42 is another argument for the involvement of this region in the interaction with DNA. 相似文献