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91.
The role of proctolin has been further investigated in the locust (Locusta migratoria) mandibular closer muscles. Radioactive calcium uptake measurements were made using protease-dissociated muscle cells. Both the phorbol ester, phorbol-12,13-dibutyrate, and proctolin produce tonic contractions which are associated with the influx of extracellular calcium. The thresholds for proctolin and the phorbol ester to contract the muscle were 1-10 nM and 10-100nM, respectively, while their respective thresholds for evoking measurable calcium influx into the muscle cells were 0.1-1 nM for proctolin, and 0.1-1 pM for phorbol-12,13-dibutyrate. The effect of phorbol-12,13-dibutyrate is blocked by a number of protein kinase inhibitors (at a concentration of 0.1 mM), suggesting that an activation of a protein kinase can lead to calcium influx. These inhibitors, however, do not block the effect of proctolin, indicating that these two compounds work through different pathways, possibly converging on the same final target. In light of this finding, a number of other compounds have been tested to try to ascertain how proctolin mediates an increased calcium influx. 相似文献
92.
93.
Formation of metabolic intermediate (MI) complexes was studied with the enantiomers of amphetamine, 1-phenyl-2-pentanamine, N-hydroxyamphetamine, and 2-nitroso-1-phenylpropane (the C-nitroso analogue of amphetamine). Three different enzyme systems were used; liver microsomes from phenobarbital pretreated rats and two reconstituted systems containing the P450 2B1 and P450 2C11 forms of cytochrome P-450. Enantioselective complex formation in microsomes was shown for the amines and the nitroso compound, but not for the hydroxylamine. The highly purified P450 2B1 system formed the MI complex with all substrates tested, and the enantioselectivity observed with the microsomal system was reproduced. In the P450 2C11 system the nitroso compounds were completely inactive, whereas the enantiomers of N-hydroxyamphetamine still produced the complex at a high rate. Changes in temperature were shown to affect (R)-2-nitroso-1-phenylpropane more than its enantiomer. Both enantiomers showed biphasic Arrhenius plots for MI complex formation in microsomes (breaks around 22 degrees C), but the activation energies of the (R)-isomer were about five times higher than those of the (S)-isomer. A theory is presented which suggests different modes of interaction with the active site of P-450 to account for the different behaviour of the various substrates. 相似文献
94.
Racemic 4',6-dichloroflavan (BW683C), a highly effective inhibitor of rhinovirus serotype 1B in vitro, was resolved by high-performance liquid chromatography on a chiral stationary phase. The enantiomers were separately collected and circular dichroism curves were obtained, in order to determine the absolute configuration of the two enantiomers. The activity of the isomers was studied on human rhinovirus serotype 1B multiplication in HeLa cell cultures, by means of the plaque reduction assay. Both enantiomers were potent inhibitors of virus replication; by comparing the IC50 values, the S form was 3.5 times more effective than the R form. 相似文献
95.
Eyvind J. Paulssen Ruth H. Paulssen Kaare M. Gautvik Jan O. Gordeladze 《Cellular signalling》1992,4(6):747-755
We have investigated the possibility that adenylyl cyclase (AC) activity and membrane protein levels of the -subunits of the stimulatory and inhibitory G-proteins of AC (Gs and Gi−2) in cultured prolactin-producing rat pituitary adenoma cells (GH3 cells) are modulated by phospholipase C (PLC)-generated second messengers. Pretreatment of cells (6–48 h) with ionomycin (1 μM) or 1-oleoyl-2-acetylglycerol (OAG; 1μM) showed that ionomycin regulated Gs levels in a time-dependent, biphasic manner; a two-fold increase followed a 40% initial reduction, while OAG lowered Gs levels by more than 50% at all time-points. Gi−2 levels remained unchanged by both pretreatments. OAG, but not ionomycin, increased basal AC activity without increasing enzyme protein levels. Alterations in AC responsiveness to peptide hormones (e.g. thyroliberin and vasoactive intestinal peptide) correlated to membrane Gs protein -subunit content. These results demonstrate the involvement of G-protein translation regulation as one mechanism of ‘cross-talk’ between the PLC- and AC-dependent signalling pathways. 相似文献
96.
Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge,NE Bavaria 总被引:4,自引:0,他引:4
Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The 13C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (13C between-25.3 and-27.8) were significantly less depleted in 13C than needles (13C between-27.3 and-29.1), and 13C in twigs increased consistently with age. The 15N values of needles ranged between-2.5 and-4.1 and varied according to stand and age. In young needles 15N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in 15N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. 15N values in twigs were more negative than in needles (-3.5 to-5.2) and showed age- and stand-dependent trends that were similar to the needles. 15N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4 in the mineral soil. The 15N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed. 相似文献
97.
Iron-efficient (WF9 corn and Coker 227 oat) and Fe-inefficient (ys1 corn and TAM 0–312 oat) cultivars were comparatively tested for their response to Fe-deficiency stress induced by the use of either ferrous or ferric chelators. Corn and oats were grown in 20 M Fe with 0, 60, and 120 M BPDS and 40 M Fe with 0, 120, and 240 M BPDS and 20 M Fe with 0 and 40 M EDDHA. All four cultivars tested, both Fe-efficient and Fe-inefficient, continuously reduced Fe3+ to Fe2+ at a low level as evidenced by the production of Fe2+ (BPDS)3 in test nutrient solutions over time. Severity of chlorosis increased as more BPDS was added to the nutrient solutions for both WF9 and ys1 corn, but unlike corn, Coker 227 and TAM 0-312 oats were both able to obtain Fe from the Fe2+ (BPDS)3 complex and were less chlorotic as a result. In short-term (4-hour) in vivo measurements, iron-stressed WF9 (Fe-efficient) corn reduced more Fe3+ to Fe2+ than similarly stressed ys1 corn, Coker 227 oat or TAM 0-312 oat. Thus, at the same time that Fe-efficient WF9 corn reduces more Fe than the other cultivars, it is also unable to compete with BPDS for that Fe in the nutrient solution. These differences coupled with the observation that only Coker 227 oat produced measureable iron solubilizing substances (phytosiderophores) suggest that these two species differ in their mechanisms for obtaining Fe during Fe-deficiency stress. 相似文献
98.
Ayumi Ohsaki Yoshihisa Kasetani Yukihiro Asaka Kozo Shibata Takashi Tokoroyama Takashi Kubota 《Phytochemistry》1991,30(12):4075-4077
Three trans-clerodane diterpenoids, pilosanol A, B and C, the last compound being a glucoside, have been isolated from the roots of Portulaca pilosa. They show a marked contrast in skeletal type with the constituents of aerial part. Evolutionary changes in the biosynthetic abilities of Portulaca species is discussed. 相似文献
99.
Maria Ransjö 《Bioscience reports》1991,11(4):203-211
The protein kinase C-(PKC) activating phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA; 100 nmol/l) and phorbol 12, 13-dibutyrate (PDBU; 100 nmol/l) enhanced basal cyclin AMP accumulation in cultured neonatal mouse calvaria. The cyclic AMP response to parathyroid hormone (PTH; 10 nmol/l) and the adenylate cyclase activators forskolin (1–3 mol/l) and choleratoxin (0.1 mg/ml) was potentiated in a more than additive manner by TPA and PDBU. In contrast, phorbol 13-monoacetate (phorb-13; 100 nmol/l), a related compound but inactive on PKC, had no effect on basal or stimulated cyclic AMP accumulation. In the presence of indomethacin (1mol/l), TPA and PDBU had no effect on cyclic AMP accumulation in calvarial bones per se, but were still able to cause a significant enhancement of the response to PTH, forskolin and choleratoxin. PTH-, forskolin- and choleratoxin-stimulated cyclic AMP accumulation in rat osteosarcoma cells UMR 106-01 was synergistically potentiated by TPA and PDBU, but not by phorb.-13. These data indicate that PKC enhances cyclic AMP formation and that the level of interaction may be at, or distal to, adenylate cyclase. 相似文献
100.
Summary A simple E.COSY type technique is described for measurement of two-bond JCOH coupling constants in proteins that are uniformly enriched with13C. The method has been used to measure2JCOH for 132 residues in the proteins calmodulin and staphylococcal nuclease having non-overlapping H–C correlations. Measured2JCOH coupling constants fall in the 0 to –9.5 Hz range. A separate experiment, measuring the accuracy of these values, indicates a root-mean-square error of 1 Hz. Comparison of the J couplings with the dihedral back bone angles from crystallographic studies confirms a weak but statistically significant correlation between the dihedral angle and the magnitude of2JCOH, but also indicates that parameters other than have a significant effect on the value of the coupling. 相似文献