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61.
Phosphate Transport across the Plasma Membrane of Wheat Leaf Protoplasts: Characteristics and Inhibitor Specificities 总被引:1,自引:1,他引:0 下载免费PDF全文
The kinetics and inhibitor specificities of phosphate transport across the plasma membrane of wheat leaf mesophyll protoplasts have been examined. Studies were also carried out on the effects of light and pH on phosphate transport and the plasma membrane electropotential. At pH 5.8 (30°C), protoplasts accumulated phosphate at the rate of 3.9 ± 0.2 nanomoles per milligram protein per hour. Phosphate uptake rates and inhibitor specificities for the leaf cell plasma membrane phosphate transporter were qualitatively similar to those observed with root protoplasts. Neither picrylsulfonic acid, or p-chloromercuribenzene sulfonate affected phosphate uptake significantly at 0.1 millimolar. Of all compounds tested, carbonyl cyanide-p-trifluoromethoxy phenylhydrazone was the most effective inhibitor of phosphate uptake (60% at 0.1 millimolar). Tribenzylphosphate inhibited uptake by 34% while dibenzylphosphate had no effect. The plasma membrane electropotential was found to be −37 ± 3 millivolts. Initiation of photosynthesis lowered the membrane potential to −39 ± 3 millivolts. Inhibition of phosphate uptake by 34% with the substrate analog tribenzylphosphate resulted in a measured membrane potential of −33 ± 3 millivolts. These changes in potential were not significant at the 5% probability level. Phosphate uptake rates remained constant under photosynthetic and nonphotosynthetic conditions. The utility of tribenzylphosphate as an inhibitor in plant systems is demonstrated. 相似文献
62.
c-Ha-ras-1 proto-oncogene amplification and overexpression during the limited replicative life span of normal human fibroblasts 总被引:6,自引:0,他引:6
A Srivastava J S Norris R J Shmookler Reis S Goldstein 《The Journal of biological chemistry》1985,260(10):6404-6409
The cellular proto-oncogene c-Ha-ras-1 undergoes up to 4-fold amplification during the limited replicative life span of normal human diploid fibroblasts in vitro. Levels of c-Ha-ras-1 messenger RNA and its p21 protein product are correspondingly elevated. Cellular proto-oncogene amplification and overexpression, although frequently associated with tumorigenesis, may thus occur during normal cellular growth. 相似文献
63.
Stability of multienzyme systems with feedback regulation has been analyzed on the basis of the Lienard-Chipart criteria. The rules governing the topological graph construction for multienzyme systems have been developed. A theorem about correspondence of the graph constructed and coefficients of the characteristic polynomial of linearized kinetic equations is proved. The graph-theoretical stability analysis proposed is illustrated by a number of examples of multienzyme systems with feedback regulation. 相似文献
64.
A. A. J. Verhofstad R. E. Coupland T. R. Parker M. Goldstein 《Cell and tissue research》1985,242(2):233-243
Summary The pre- and postnatal development of the adrenal medulla was examined in the rat by immunohistochemistry and by assay of catecholamines. Immunohistochemistry involved the use of antibodies to noradrenaline (NA), adrenaline (A) and the biosynthesizing enzymes dopamine -hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT). Adrenal glands were obtained from animals from the 16th day of gestation to the 7th postnatal day at daily intervals, and at the 14th postnatal day, and from adult rats. Tissues were fixed in ice-cold, 4% paraformaldehyde, buffered at pH 7.3. Cryostat sections (7 m) were stained with the indirect immunofluorescence technique. Adrenals from the same developmental stages were assayed for the presence of DA (dopamine), NA and A by ion-pair reversed-phase liquid chromatography with electrochemical detection.In adult adrenals the majority of the medullary cells (approximately 80%) were highly immunoreactive to A and moderately immunoreactive to NA. They also showed immunoreactivity to both DBH and PNMT, i.e., they are synthesizing and storing A. The remaining cell clusters were only stained by antibodies to DBH and NA (NA-synthesizing and -storing cells). These findings correlate well with the relative concentrations of A and NA as determined by assay.Three developmental phases could be distinguished. In the first phase, the 16th and 17th prenatal day, medullary cells were only immunoreactive to DBH and NA, and only very small amounts of A as compared to NA were found. During the second period, from the 18th prenatal day to 2 or 3 days after birth, all medullary cells were immunoreactive to DBH, NA, PNMT and A, and during this phase the adrenaline concentration increased daily and became the predominant amine on the 20th day of gestation. Adrenaline represented 75% of total catecholamine on the 1st to 3rd day after birth. The third phase started at the 2nd or 3rd postnatal day and was characterized by the presence of an increasing number of medullary cells solely immunoreactive to DBH and NA, hence synthesizing and storing NA. The remaining cells were immunoreactive to DBH, NA, PNMT and A. Postnatally, the relative concentration of A continued to rise reaching 79% by the 4th postnatal day. These results indicate that initially the adrenal medullary cells are synthesizing and storing almost exclusively NA. Probably, adrenaline synthesis begins at the 16th–17th day of gestation and the cells are then capable of synthesizing and storing both NA and A (mixed cell type) with A synthesis and storage rapidly becoming predominant. Finally, after birth, separate NA-synthesizing and -storing cell types are formed and the so-called A cells stored predominantly (probably >90%) adrenaline with a small proportion of noradrenaline.In the medullary blastema and in the sympathetic ganglia of prenatal animals two cell types, only immunoreactive to DBH and NA, were observed. Presumably, these cells represent developing sympathetic neurons and extra-adrenal chromaffin cells; the latter cell type occasionally invades the adrenal gland. Thus, prospective medullary cells are able to synthesize and store NA before they have made contact with the cortical blastema but A-synthesizing cells are found only within the adrenal gland.Low but significant amounts of DA were found in the adrenal before birth and during the first two postnatal weeks but in the adult animal this accounted for less than 0.1% of total catecholamine.Preliminary reports of this study were made to the American Association of Anatomists (Anat. Rec. 196; 196A, 1980), the Dutch Anatomical Society (Acta Morphol. Neerl. Scand. 19; 330, 1981, and the XIIIth Acta Endocrinologica Congress (Acta Endocrinol. 97: Suppl. 243, 285, 1981) 相似文献
65.
W S Yamanashi D W Anderson P D Lester D Herrick J W Frazer 《Physiological chemistry and physics and medical NMR》1985,17(1):81-100
Magnetic resonance image (MRI) pixel intensities were investigated using a phantom containing several uniform size chambers filled with solutions of known relaxation times, as well as head scans of patients and volunteers. Intensities were measured with a variety of pulse intervals typically used for imaging with spin echo, (SE) and inversion recovery (IR) sequences at 0.15 Tesla using the back projection (R-THETA) method, and at 0.27 Tesla using the 2-dimensional Fourier transform (2DFT) technique. The results were compared with the calculated dependence of MRI signal intensity on relaxation times and pulse interval parameters using the well known functions containing exponential forms. The experimental and the calculated pixel intensity time dependence did not always agree. We infer that factors other than the conventional functions for T1 and T2 signal decay are important. These factors may include the attenuation of the radiofrequency (RF) signals through inhomogenious lossy dielectric materials (e.g., tissues and organs), the location (coordinate) of the portion of the sample to be imaged relative to the RF coils, and the timing and amplitude of gradient pulses relative to the RF input and the detected signals. The flow velocity and diffusions are also important determinants of the signal from blood vessels and body fluids. We point out the necessity for further investigation toward more comprehensive understanding of MRI intensities. 相似文献
66.
F Takusagawa B M Goldstein S Youngster R A Jones H M Berman 《The Journal of biological chemistry》1984,259(8):4714-4715
Crystals of a 2:1 complex between the self-complementary DNA hexamer d(ATGCAT) and the antitumor drug actinomycin D have been grown from solutions of polyethylene glycol 400. The crystals are orthorhombic with space group P2(1)2(1)2(1) and a = 95.6, b = 42.7, and c = 40.8 A. A Patterson map calculated from preliminary diffractometer data as well as packing considerations suggest a model in which the actinomycin D is intercalated into a double-stranded DNA hexamer. There are four such complexes in the asymmetric unit. 相似文献
67.
Teresa de Sa E Melo Patrice Morlière Sonia Goldstein René Santus Louis Dubertret Dominique Lagrange 《Biochemical and biophysical research communications》1984,120(2):670-676
5-methoxypsoralen (5-MOP) binds to human serum low density lipoproteins (LDL) according to a two-step process. Scatchard analysis of the first step yields K = 1.4 × 105 M?1 and 4 binding sites. It involves the LDL apoprotein. The second step corresponds to a solubilization, in the lipidic core, of ? 45 molecules of 5MOP per LDL molecule. It is accompanied by a large blue shift of the 5MOP fluorescence. The ability of LDL to bind 5MOP and to carry it into various cells may explain some biological effects sometimes encountered during PUVA therapy. 相似文献
68.
Phorbol esters inhibit the binding of low-density lipoproteins (LDL) to U-937 monocytelike cells 总被引:2,自引:0,他引:2
M Rouis S Goldstein P Thomopoulos M Berthelier C Hervy U Testa 《Journal of cellular physiology》1984,121(3):540-546
The present study demonstrates that U-937 monocytelike human cells possess specific LDL receptors. 125I-LDL binds at 4 degrees C on the cell surface. The bound molecules are releasable by heparin. The reaction requires Ca2+ and the binding sites are sensitive to proteolysis. Unlabeled LDL compete with 125I-LDL, whereas HDL are ineffective. At 37 degrees C, LDL are internalized and degraded by a chloroquine-sensitive pathway. Tumor-promoting phorbol esters inhibit the binding of 125I-LDL to its receptor on U-937 cells. This inhibition exhibits temperature, time, and concentration dependence. At 37 degrees C, inhibition is 50% at 5 X 10(-9) M of TPA. After removal of phorbol esters, treated cells recover their 125I-LDL-binding activity in 60 min. The inhibitory activities of various phorbol esters are proportional to their tumor-promoting activities. Inhibition appears to be due to a reduction in the number of available LDL receptors rather than a decrease in receptor affinity. 相似文献
69.
70.
Neuropeptide Y,enkephalin and noradrenaline coexist in sympathetic neurons innervating the bovine spleen 总被引:4,自引:0,他引:4
Dr. G. Fried L. Terenius E. Brodin S. Efendic G. Dockray J. Fahrenkrug M. Goldstein T. Hökfelt 《Cell and tissue research》1986,243(3):495-508
Summary The subcellular distribution of noradrenaline (NA), neuropeptide Y (NPY), Met and Leu-enkephalin (ENK), substance P (SP), somatostatin (SOM), and vasoactive intestinal polypeptide (VIP) was investigated in homogenates of bovine splenic nerve. The distribution of noradrenergic peptide-containing nerves in the bovine celiac ganglion, splenic nerve and terminal areas in spleen was studied by indirect immunofluorescence histochemistry using antisera to tyrosine hydroxylase (TH), dopamine--hydroxylase (DBH), NPY, enkephalin peptides, SP, SOM, VIP and peptide HI (PHI).After density gradient centrifugation, high levels of NPY and ENK-like immunoreactivity (LI) were found in high-density gradient fractions, coinciding with the main NA peak. SP, SOM and VIP were found in fractions with a lower density, VIP being also enriched in a heavy fraction; the latter three peptides were present in low concentrations.Immunohistochemistry revealed that staining for NPYLI and ENK-LI partly overlapped that for TH and DBH in celiac ganglia, splenic nerve axons and terminal areas of spleen. Almost all principal ganglion cells were TH- and DBH-immunoreactive. Many were also NPY-immunoreactive, whereas a smaller number were ENK-positive. In the celiac ganglion patches of dense SP-positive networks and some VIP/PHI- and ENK-immunoreactive fibers were seen around cell bodies.The results indicate that NPY and ENK are stored with NA in large dense-cored vesicles in unmyelinated axons of bovine splenic nerve. SP, SOM and VIP appear in different organelles in axon populations separate from sympathetic noradrenergic nerves. 相似文献