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91.
The coat protein of coliphage M13 is an integral protein of the host-cell cytoplasmic membrane prior to its assembly into virions. It is initially synthesized as procoat, a soluble precursor with a 23 amino acid leader sequence at its amino terminus. 35S-labeled procoat accumulates during an in vitro translation reaction that contains 35S-methionine and RNA from M13-infected cells. Radiochemically pure procoat has been isolated from in vitro translation reactions by extraction into an organic solvent and gel filtration through Sephadex LH-60. Radiochemically pure procoat can be used as substrate in rapid and quantitative assays for leader peptidase and for leader peptide hydrolase, an enzyme that degrades the leader peptide after its release from procoat. Procoat solubility, digestion by leader peptidase and processing by membranes are affected by the presence of Mg2+ ion. Isolated procoat is soluble in water at low ionic strength and mildly alkaline pH as well as in detergent solutions. It is cleaved to coat protein by purified E. coli leader peptidase and by inverted E. coli inner-membrane vesicles. These properties of the purified procoat mirror those of the procoat in crude extracts. This suggests that there are no other soluble components that are necessary for the assembly of procoat into the membrane and its conversion to coat; specifically, it provides powerful evidence that protein synthesis is not involved. 相似文献
92.
Independently derived mutants of Chinese hamster ovary cells have been isolated and shown to exhibit a subtle glycosylation defect resulting in the premature termination of certain asparagine-linked carbohydrate moieties. This carbohydrate alteration is akin to the types of structural variation termed microheterogeneity and is thought not to affect the biological activities of glycoproteins that manifest the phenomenon. However, the carbohydrate change expressed by the mutants is stable and heritable, and 1251-lectin-binding studies suggest that it profoundly alters their surface recognition properties. The mutation appears to affect a specific subpopulation of galactose residues in asparagine-linked carbohydrate of the type found associated with the G glycoprotein of vesicular stomatitis virus. The mutant cells also exhibit morphological changes in substratum culture. 相似文献
93.
Summary The amounts of DNA in haploid and diploid cells of Drosophila melanogaster have been determined by DNA-Feulgen cytophotometry, using Xenopus laevis erythrocyte nuclei as a reference standard. The haploid male genome is estimated to be 0.18 pg DNA and the haploid female genome, 0.20 pg DNA. 相似文献
94.
One question which is unresolved in developmental immunology is whether cortical thymocytes are the precursor cells which give rise to medullary thymocytes and peripheral T cells. Cortical thymocytes display a characteristic surface antigen phenotype (high TL and Thy-1, low H-2, no Qa-2, no Qa-3), are agglutinated by peanut agglutinin (PNA), and are unresponsive to concanavalin A (Con-A). The functionally more mature medullary thymocytes express a surface phenotype more closely resembling peripheral T cells (no TL, low Thy-1, high H-2, and some Qa-2), are not agglutinated by PNA, and are responsive to Con-A. An in vitro induction system has been devised in which mouse thymocytes undergo quantitative changes in surface antigens in less than 24 hr and increase their mitogen response to Con-A. The phenotypic changes are characterized by a decrease of TL and Thy-1 and an increase in H-2, Qa-2, and Qa-3. Studies in which thymocytes were fractionated on BSA gradients and by PNA agglutination demonstrate that the inducible cells have the properties of cortical thymocytes. Our data show that a subpopulation of cortical thymocytes can acquire phenotypic characteristics similar to medullary thymocytes and peripheral T cells. 相似文献
95.
Embryo transfer experiments were carried out to study the developmental capacity of cultured rabbit embryos when transferred to recipients of variable postovulatory maturity. Rabbit embryos were flushed from the oviduct at 26 hours postcoitum (pc) and cultured in a modified Ham's F-10 medium supplemented with bovine serum albumin (BSA) for a period of 70 hours. At 96 hours pc the cultured embryos, which ranged from the early morula to the expanding blastocyst stage, were transferred to pseudopregnant recipients mated to vasectomized males 36 to 96 hours prior to the transfer procedure. Greatest embryo survival occurred when transfers were made to either the oviducts or uterine horns of recipients at 48 hours pc. Intermediate results for both implantation rates and number of young born were obtained with recipients at 36, 60, 72, and 84 hours pc. Transferred embryos consistently failed to survive the uterine environment of recipients 96 hours pc at transfer although this group was synchronous with embryonic chronological age. Oviductal transfers were generally more successful than uterine transfers. Markedly higher rates of embryo survival resulted from embryos that were collected 60 and 72 hours pc and transferred directly to synchronous recipients without an interim period of culture. Dissimilarity of development for in vivo grown rabbit embryos and those cultured in synthetic medium is demonstrated. 相似文献
96.
Elizabeth M.K. Leovey Niels H. Andersen Pamela Bissonette 《Prostaglandins & other lipid mediators》1979,17(1)
, originally introduced as an inadvertent contaminant in solutions used for evaluating the stability of prostaglandins, proved to lead to the rapid disappearance of the cyclopentenone unit of PGA2 (as monitored by circular dichroic spectroscopy). The cyclopentenone unit is converted, in various metabolites, to a 9-keto, 9α or 9β-hydroxy group lacking the ring unsaturation. The major EtoAc-soluble 9-hydroxy metabolite (Compound-I) was shown to be 9α, 15α-dihydroxy-2,3,4,5-tetranor-13-
-prostenoic acid. Similar tetranor 9-hydroxy metabolites with one additional degree of unsaturation, and with a 9β-hydroxy group, also occur but these have not been fully characterized. Only two of the wide range of 9-keto metabolites are fully characterized by mass spectral (MS) data: 9,15-oxo-2,3,4,5-tetranorprostanoic acid and 9,15-oxo-2,3,4,5-tetranor-13-
-prostenoic acid. The water soluble metabolites have not been characterized further.The fully characterized metabolites together with MS data from mixtures of minor metabolites indicate that
can perform the following transformations: β-oxidation, dehydrogenation at C-15, reduction of the enone carbon-carbon double bonds (both Δ10,11 and Δ13,14), reduction of the 9-ketone, and possibly migration of the cyclopentyl double bond (Δ10,11 → Δ11,12).
metabolizes 15-epimeric PGA2 equally readily with the production of similar products. PGA1 affords less 9-keto metabolites with compound I constituting 33% of the product by HPLC analysis.
displays some enantioselectivity, PGA2 and 15-epi-PGA2 are each metabolized more rapidly than their enantiomers. Other prostaglandins appear to be less readily metabolized. 相似文献
97.
Pamela D. Green C.Richard Savage Charles A. Hall 《Archives of biochemistry and biophysics》1976,176(2):683-689
Mouse fibroblast (L-929) cells, in culture, synthesized and secreted into the growth medium a vitamin B12-binding substance which was identical to mouse transcobalamin II (TC II) as judged by the following criteria: (i) gel filtration on Sephadex G-200, (ii) ion-exchange chromatography on DEAE-cellulose and CM-cellulose, and (iii) the ability to facilitate cellular B12 uptake by L-929 cells. The secretion of mouse fibroblast binder was blocked by cycloheximide and puromycin; and in both cases the cells' ability to secrete this binder was partially restored when the inhibitor was removed. Within 30 h after the cells were exposed to [57Co]B12 bound to mouse serum TC II (Mr ~ 38,000) the [57Co]B12 was bound to a large molecular weight intracellular binder (Mr ~ 120,000) which was not released into the culture medium. During this same incubation period, the cells released free [57Co]B12 and [57Co]B12 bound to a protein which had the same elution volume as mouse serum TC II on Sephadex G-200. 相似文献
98.
A mutant form of erythrocyte hypoxanthine-guanine phosphoribosyltransferase with an abnormal isoenzyme pattern was found in a patient with a partial enzyme deficiency and X-linked gout. This abnormal pattern was a marker for the mutant enzyme in hemolysate from the heterozygote for the enzyme deficiency.These studies were generously supported by the Medical Research Council of Canada (MRC # MA4758) and the Canadian Arthritis and Rheumatism Society. 相似文献
99.
Pamela Dunsmuir 《Chromosoma》1976,56(2):111-125
Two distinct satellite DNAs, amounting to 25% of the total DNA, were isolated from the nuclei of the red-necked wallaby, Macropus rufogriseus. The physical properties of native, single-stranded and reassociated molecules were studied in buoyant-density gradient centrifugation. The homogeneity of each satellite fraction was examined using melting characteristics of native and reassociated DNA, and renaturation kinetics. These data suggest that sequence heterogeneity exists in both fractions. Each satellite fraction was found by in situ hybridization to be localized in heterochromatin of interphase nuclei and in the centromeric regions of metaphase chromosomes. The chromosomal distributions of the two satellite DNAs differentiate the sex chromosomes, which have sequences of only one satellite, from the autosomes which have sequences of both satellites in the centromeric heterochromatin. Giemsa C-banding techniques also showed a differentiation of the centromeric regions of sex chromosomes from those of the autosomes. 相似文献
100.
Upon irradiation in the ultraviolet region aromatic chromophores may transfer energy to a nearby Tb3+, which in turn emits a green phosphorescence. This paper reports the characterization of the ultraviolet excitation spectra of aromatic chromophores capable of transferring energy to Tb3+ by monitoring of the green Tb3+ emission in the 540-550 nm region. Results are included for complexes containing phenyl, hydroxyphenyl, indole. and catechol chromophores. Characteristic excitation spectra are presented for the aromatic chromophores occurring as side chains in proteins. Though it is preferable to compare entire excitation spectra, the ratio of intensities at 292 to 276 nm, R, is suggested as a useful diagnostic criterion. Numerical R values are indicative of the following aromatic side chains as the energy donor to Tb3+: R <0.2, unionized tyrosine; R = 0.5 to 1.0, tryptophan; and R > 1.8. ionized tyrosine. Tlie phenylalanyl chromophore displays a definitive excitation spectrum at shorter wavelengths. For ovotransferrin R = 0.9 and comparison of the full excitation spectra suggests that it contains comparable contributions from both ionized tyrosine and tryptophan side chains. Some difficulties in obtaining reliable excitation spectra are described. An analysis of inner-filtering of incident light reveals that for an absorbance less than 0.8 the excitation spectrum is broadened and flattened compared to the absorption spectrum. At maximum absorbances greater than 0.8 false maxima may appear to both sides of a real maximum. Two spurious maxima in an excitation spectrum were generated in a Tb3+ complex and compared to the correct excitation spectrum of the same complex obtained at lower absorbance. 相似文献