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1.
The role of a pertussis toxin sensitive GTP-binding protein in mediating between cholecystokinin receptors and phosphatidylinositol 4,5-bisphosphate phosphodiesterase as well as in preventing cholecystokinin from increasing cellular cyclic AMP has been investigated using dispersed acini from rabbit pancreas. Pertussis toxin pretreatment (500 ng/ml, 2 h) did not affect cholecystokinin(octapeptide) (CCK-8)-induced increases in cytosolic free Ca2+ as judged from changes in fluorescence obtained from quin2-loaded acini. Although pretreatment with pertussis toxin was also without effect on resting acinar cell cyclic AMP levels, adenylate cyclase activity was increased, since inhibition of cyclic AMP phosphodiesterase activity by isobutylmethylxanthine (IBMX) resulted in an additional increase in cyclic AMP levels in toxin-treated acini, indicating that acinar cell adenylate cyclase activity is under some tonic inhibitory control by the pertussis toxin-sensitive inhibitory GTP-binding protein (Gi) of the adenylate cyclase system. CCK-8 gave an increase in cyclic AMP levels in both control (1.6-fold) and toxin-treated (2.3-fold) acini, leading to cyclic AMP levels in the toxin-treated acini 2-times as high as those in control acini. In the presence of IBMX, the cyclic AMP response to CCK-8 was again markedly enhanced in acini pretreated with the toxin (3.2- vs. 1.8-fold), resulting in cAMP levels in the toxin-treated acini 3.7-times those in the absence of IBMX, 2.5-times those in control acini in the presence of IBMX and 7.0-times those in control acini in the absence of IBMX. Neither the pretreatment with pertussis toxin, nor the presence of IBMX alone, nor the combination had an effect on basal amylase secretion. However, all three treatments potentiated the stimulatory effect of CCK-8 on amylase secretion and the amount of potentiation was proportional to the cyclic AMP levels reached. Our findings suggest that in the intact pancreatic acinar cell Gi inhibition of the catalytic subunit of the adenylate cyclase may largely be responsible for preventing cholecystokinin from increasing cellular cyclic AMP. They moreover show that cyclic AMP is a modulatory agent in rabbit pancreatic enzyme secretion, not able to stimulate secretion itself, but potentiating effects mediated by the phosphatidylinositol-calcium pathway. 相似文献
2.
Ken B. Waites Joseph G. Tully David L. Rose Peggy A. Marriott Richard O. Davis Dr. Gail H. Cassell 《Current microbiology》1987,15(6):325-327
Acholeplasmas have been isolated from a variety of animals, insects, and plants, but onlyAcholeplasma laidlawii has previously been found in humans. We have isolatedAcholeplasma oculi in pure culture from the amniotic fluid of a woman at 19 weeks of gestation. The organism was positively identified by growth inhibition, epi-immunofluorescence, and arbutin hydrolysis. Demonstration of organisms directly in amniotic fluid by DNA fluorochrome and immunofluorescence staining provided additional evidence that the isolate was genuine and not a medium contaminant. The remainder of the pregnancy was unremarkable, and a full-term male infant was delivered without complications. Even though there is some evidence possibly associatingA. oculi with various diseases in livestock, the prevalence and significance ofA. oculi in humans has not been determined. 相似文献
3.
4.
J L Tilly H Billig K I Kowalski A J Hsueh 《Molecular endocrinology (Baltimore, Md.)》1992,6(11):1942-1950
Recent biochemical studies have suggested that apoptotic cell death is the molecular mechanism underlying the degeneration of ovarian follicles during atresia. Using a sensitive autoradiographic method for the detection of DNA fragmentation, we studied apoptosis in ovarian granulosa cells or intact follicles placed in serum-free culture as model systems to elucidate the hormonal regulation of atresia. Immature rats (25 days old) were primed for 2 days with 10 IU equine CG to induce a homogeneous population of mature preovulatory follicles. Granulosa cells isolated from these follicles contained predominantly intact high mol wt DNA. However, a time-dependent, spontaneous onset of internucleosomal DNA fragmentation characteristic of apoptotic cell death occurred in granulosa cells during culture. Treatment of granulosa cells with epidermal growth factor (EGF), transforming growth factor-alpha (TGF alpha), or basic fibroblast growth factor (bFGF) inhibited the spontaneous onset of apoptotic DNA cleavage found during culture by 40-60%. In contrast, insulin-like growth factor I, insulin, TGF beta and tumor necrosis factor-alpha were ineffective. Likewise, activation of the protein kinase A or C pathways with forskolin or phorbol 12-myristate 13-acetate, respectively, did not prevent the onset of DNA fragmentation, although inclusion of a tyrosine kinase inhibitor (genistein) completely blocked the ability of EGF, TGF alpha, and bFGF to suppress apoptosis in granulosa cells. Similar to cultured granulosa cells, a spontaneous onset of apoptosis was also observed to occur in isolated preovulatory follicles during culture. Furthermore, treatment of follicles with EGF or bFGF inhibited the spontaneous initiation of apoptosis, and the suppressive effects of these growth factors were also attenuated by co-treatment with genistein.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
5.
Identification and localization of proteins encoded by two DIF-inducible genes of Dictyostelium 总被引:3,自引:0,他引:3
We show that pDd56 and pDd63, two related DIF-inducible genes of Dictyostelium, respectively encode the ST310 and ST430 polypeptides identified by Morrissey, Devine, and Loomis (1984, Dev. Biol. 103, 414-424). We localize the two proteins by immunoelectron microscopy to the extracellular matrix surrounding the stalk cells and the stalk tube. Coupled with their predicted amino acid sequence and biochemical properties, this suggests that they are structural proteins of the stalk. 相似文献
6.
7.
Prostatic steroid-binding protein, whose expression is stimulated by androgens, consists of two subunits, one containing the polypeptides C1 and C3 and the other containing the polypeptides C2 and C3. We have isolated and sequenced cDNA clones specific for C3 mRNA and used them to isolate and characterize genomic clones for two C3 genes. Both genes are 3.2 kilobases with identical exon/intron arrangements, which is similar to the organization of the C1 and C2 genes, suggesting that they may have arisen by duplications of an ancestral gene. Finally, homologous human genes have not been detected. 相似文献
8.
9.
Peggy Keeling Keith Johnson Daryl Sas Kathleen Klukas Peter Donahue Ross Johnson 《The Journal of membrane biology》1983,74(3):217-228
Summary The major membrane protein of the bovine lens fiber cell is a 26-kilodalton (kD) protein (MP26), which appears to be a component
of the extensive junctional specializations found in these cells. To examine the arrangement of MP26 within the junctional
membranes, various proteases were incubated with fiber cell membranes that had been isolated with or without urea and/or detergents.
These membranes were analyzed with electron microscopy and SDS-PAGE to determine whether the junctional specializations or
the proteins were altered by proteolysis. Microscopy revealed no obvious structural changes. Electrophoresis showed that chymotrypsin,
papain, and trypsin degraded MP26 to 21–22 kD species. A variety of protease treatments, including overnight digestions, failed
to generate additional proteolysis. Regions on MP26 which were sensitive to these three proteases overlapped. Smaller peptides
were cleaved from MP26 with V8 protease and carboxypptidases A and B. Protein domains cleaved by these proteases also overlapped
with regions sensitive to chymotrypsin, papain, and trypsin. Specific inhibition of the carboxypeptidases suggested that cleavage
obtained with these preparations was not likely due to contaminating endoproteases. Since antibodies are not thought to readily
penetrate the 2–3 nm extracellular gap in the fiber cell junctions, antibodies to MP26 were used to analyze the location of
the protease-sensitive domains. Antisera were applied to control (26 kD) and proteolyzed (22 kD) membranes, with binding being
evaluated by means of ELISA reactions on intact membranes. Antibody labeling was also done following SDS-PAGE and transfer
to derivatized paper. Both assays showed a significant decrease in binding following proteolysis, with the 22 kD product showing
no reaction with the anti-MP26 sera. These investigations suggest that MP26 is arranged with approximately fourfifths of the
primary sequence “protected” by the lipid bilayer and the narrow extracellular gap. One-fifth of the molecule, including the
C-terminus, appears to be exposed on the cytoplasmic side of the membrane. 相似文献
10.
The dnaK protein modulates the heat-shock response of Escherichia coli 总被引:49,自引:0,他引:49
E. coli bacteria respond to a sudden upward shift in temperature by transiently overproducing a small subset of their proteins, one of which is the product of the dnaK gene. Mutations in dnaK have been previously shown to affect both DNA and RNA synthesis in E. coli. Bacteria carrying the dnaK756 mutation fail to turn off the heat-shock response at 43 degrees C. Instead, they continue to synthesize the heat-shock proteins in large amounts and underproduce other proteins. Both reversion and P1 transduction analyses have shown that the failure to turn off the heat-shock response is the result of the dnaK756 mutation. In addition, bacteria that overproduce the dnaK protein at all temperatures undergo a drastically reduced heat-shock response at high temperature. We conclude that the dnaK protein is an inhibitor of the heat-shock response in E. coli. 相似文献