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11.
12.
Ion-Exchange Chromatography Separates Activities Synthesizing and Degrading Fructose 2,6-Bisphosphate from C3 and C4 Leaves but Not from Rat Liver 总被引:1,自引:1,他引:0
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Fructose-6-phosphate,2-kinase and fructose-2,6-bisphosphatase were separated on the basis of charge from leaves of C3 (spinach, lettuce, and pea) and C4 (sorghum and amaranthus) plants but not from rat liver—a tissue known to contain a bifunctional enzyme with both activities. [2-32P]Fructose 2,6-bisphosphate binding experiments also suggest that the major forms of these activities reside on different proteins in leaves. 相似文献
13.
Continuous high density expression of human beta 2-adrenergic receptors in a mouse cell line previously lacking beta-receptors 总被引:1,自引:0,他引:1
The PvuII fragment of human genomic clone LCV-517 which contains the entire coding region of a beta-adrenergic receptor gene was cloned into the SmaI site of the expression vector pMSG. The recombinant DNA was cotransfected with pRSVneo into mouse B-82 cells using the CaPO4 precipitation method. B-82 cells do not possess beta-adrenergic receptors but do contain prostaglandin E1 receptors that stimulate adenylate cyclase. Following transfection, several colonies expressing beta-adrenergic receptors were isolated. Analysis of ligand binding to expressed beta-receptors indicated that the protein encoded by the gene in clone LCV-517 was a beta 2-adrenergic subtype. Human beta 2-adrenergic receptors photoaffinity labeled with [125I]iodocyanopindolol diazirine migrated on sodium dodecyl sulfate-polyacrylamide gels consistent with a molecular mass of 68,000, demonstrating that the receptor is glycosylated to an extent of 25-30% by weight. Addition of isoproterenol to cultures of transfected cells resulted in a 3-4-fold stimulation of adenylate cyclase, an effect similar to that seen in control B-82 cells with prostaglandin E1. These data describe the production of stable murine clonal cell lines expressing human beta 2-adrenergic receptors and illustrate the utility of such lines in the biochemical and pharmacological characterization of receptor proteins. 相似文献
14.
The mechanism underlying the association of rising concentrations of circulating triiodothyronine (T3) with the prepartum surge in the concentration of cortisol was investigated in 11 fetal sheep. The concentrations and metabolic clearance rates of T3 and thyroxine (T4) were measured prior to and following a continuous intravascular infusion of cortisol (1 mg/h for 84 h). Mean plasma T3 concentrations increased 10-fold following cortisol infusion whereas the concentrations of T4 either remained stable or exhibited a variable decline. Cortisol induced a 5-fold decrease in the metabolic clearance rate of T3 and a 6-fold increase in that of T4. The corresponding mean production rates of T3 and T4 increased significantly although the magnitude of the change varied between fetuses. We conclude that the prepartum rise in plasma T3 concentrations is likely to be a consequence of both a decreased metabolic clearance of T3 and increased peripheral conversion of T4 to T3 caused by rising concentrations of cortisol in fetal plasma. 相似文献
15.
Hypothalamic contents of gonadotropin-releasing hormone (GnRH) in neonatally orchidectomized infant, juvenile, and adult monkeys were measured by a radioimmunoassay (RIA) and by an in vivo bioassay that utilized luteinizing hormone (LH) secretion in estrogen- and progesterone-treated ovariectomized rats. The results of the bioassay provided no evidence to suggest that hypothalamic GnRH content in juvenile monkeys (mean = 83 ng/hypothalamus; n = 3) was less than that in infants (mean = 54 ng/hypothalamus; n = 4) and adults (mean = 36 ng/hypothalamus; n = 3). A similar developmental pattern in hypothalamic GnRH content was also observed when the decapeptide was measured by RIA. In striking contrast to the maintenance of hypothalamic GnRH content throughout postnatal development, pituitary gonadotropin contents and serum gonadotropin concentrations were markedly reduced in juvenile monkeys. 相似文献
16.
Expression of human plasminogen cDNA in a baculovirus vector-infected insect cell system 总被引:5,自引:0,他引:5
J Whitefleet-Smith E Rosen J McLinden V A Ploplis M J Fraser J E Tomlinson J W McLean F J Castellino 《Archives of biochemistry and biophysics》1989,271(2):390-399
A cDNA that encodes the human plasminogen (HPg) amino acid sequence has been inserted adjacent to the polyhedrin promoter in the genome of the baculovirus, Autographa californica nuclear polyhedrosis virus, which was then used to infect cultured cells of the farm armyworm, Spodoptera frugiperda. Under the conditions of cell growth employed, recombinant (rec)-HPg was secreted into the medium after 24 h postinfection (p.i.), at which point virtually no rec-HPg antigen remained inside the cells. At 48 h p.i., a maximal level of intact rec-HPg was present in the medium, which underwent substantial proteolytic digestion after that time. The rec-HPg produced by this expression system possessed a molecular weight equivalent to that of plasma [Glu1]-plasminogen. In addition, the rec-HPg adsorbed to Sepharose-lysine, and was eluted with epsilon-aminocaproic acid (EACA). The recombinant protein also interacted with polyclonal antibodies generated to plasma HPg, as well as with a monoclonal antibody directed against a distinct region (kringle 1-3) of the plasma HPg molecule. Finally, the insect-expressed rec-HPg was activatable to plasmin (HPm) by urokinase. The results demonstrate that this expression system produces a full-length functional single-chain rec-HPg, which can be isolated intact from the culture medium, with some consideration for the temporal events that occur in secretion and longer-term degradation of the protein. The fact that this rec-HPg was converted to HPm with a plasminogen activator, and that it interacted with anti-plasma HPg polyclonal and monoclonal antibodies, as well as with the ligand, EACA, indicates that the molecule retains many of its important functional properties and is folded in an integral manner. 相似文献
17.
Endo-exonuclease of Aspergillus nidulans 总被引:1,自引:0,他引:1
Endo-exonuclease (EE) has been found in both active and inactive, but trypsin-activatable, forms in Aspergillus nidulans. Active EE was present mainly in nuclei, mitochondria, and vacuoles, while trypsin-activatable EE was mainly in the cytosol. The active form accounts for over 90% of the neutral deoxyribonuclease activity extracted from mycelia. A single strand (ss) DNA-binding EE associated with a 28 kilodalton (kDa) polypeptide was partially purified and characterized. It was found to closely resemble, in size and enzymological properties, the ss-DNA-binding EE previously purified from Neurospora crassa. Aspergillus nidulans EE was also found to be immunochemically related to the N. crassa EE and, like that enzyme, was probably derived from a polypeptide of 90 kDa or larger through proteolysis during extraction and purification. It had divalent metal ion-dependent (Mg2+, Mn2+, or Zn2+) activity on both DNA and RNA, which ultimately produced small 5'-P-terminated oligonucleotides. The nuclease activity was mixed endo- and exo-nucleolytic with ss-DNA as substrate, but largely exonucleolytic with double strand (ds) DNA. Superhelical phi X-174 DNA was nicked by EE to form relaxed circular and then linear ds-DNA, which was rapidly degraded to shorter fragments. Linearized pBR322 DNA was extensively nicked internally under conditions where there was relatively low exonuclease activity, but this nicking required that 5'-P-termini be present on the linear ds-DNA. The levels of active EE found in extracts of two recombination-deficient mutants of A. nidulans, uvsC and uvsE, dit not differ significantly from those in extracts of the wild type. 相似文献
18.
Differential methylation of the hypervariable locus DXS255 on active and inactive X chromosomes correlates with the expression of a human X-linked gene 总被引:15,自引:0,他引:15
Consistent differences in methylation of particular cytosine residues in the DNA of active and inactive X chromosomes can be used for rapid, direct analysis of X-inactivation patterns in different female tissues. We have studied methylation of the highly polymorphic DXS255 locus in tissues from patients with deficiency of the E1 alpha subunit of the pyruvate dehydrogenase complex in whom the results can be correlated directly with total enzyme activity, levels of immunoreactive protein, and patterns of cell mosaicism. The results confirm that methylation of the DXS255 locus correlates with X-chromosome expression. In patients and normal controls, the pattern of X inactivation varied widely from tissue to tissue and often deviated markedly from a 50:50 proportion. These deviations are likely to reflect small numbers of tissue-specific stem cells at the time of random X inactivation and cannot be taken alone as evidence for selection or "nonrandom" inactivation. 相似文献
19.
Dynamic changes in optic fiber terminal arbors lead to retinotopic map formation: an in vivo confocal microscopic study 总被引:2,自引:0,他引:2
Dynamic remodeling of retinal ganglion cell terminal arbors has been proposed to contribute to formation of the topographically ordered retinotectal projection. To test this directly, the growth of individual terminal arbors was observed in live X. laevis tadpoles using a confocal microscope to visualize their complex three-dimensional structure. During initial development, nasal and temporal retinal arbors covered overlapping tectal areas. Despite subsequent remodeling, the dimensions and positions of the temporal arbors remained relatively stable. In contrast, the nasal arbors grew caudally, as they extended caudal branches and retracted rostral branches. These results suggest that differences in the remodeling of the nasal and temporal arbors lead to the emergence of retino-topography along the rostrocaudal axis of the tectum. All the terminal arbors were dynamic, including those with stable dimensions, suggesting that continual remodeling of arbors may be a universal feature of neuronal projections. 相似文献
20.