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71.
Daniela L Catalano Dupuy Daniela V Rial Eduardo A Ceccarelli 《European journal of biochemistry》2004,271(22):4582-4593
Ferredoxin-NADP(H) reductases (FNRs) represent a prototype of enzymes involved in numerous metabolic pathways. We found that pea FNR ferricyanide diaphorase activity was inhibited by Zn2+ (Ki 1.57 microM). Dichlorophenolindophenol diaphorase activity was also inhibited by Zn2+ (Ki 1.80 microM), but the addition of ferrocyanide was required, indicating that the inhibitor is an arrangement of both ions. Escherichia coli FNR was also inhibited by Zn-ferrocyanide, suggesting that inhibition is a consequence of common structural features of these flavoenzymes. The inhibitor behaves in a noncompetitive manner for NADPH and for artificial electron acceptors. Analysis of the oxidation state of the flavin during catalysis in the presence of the inhibitor suggests that the electron-transfer process between NADPH and the flavin is not significantly altered, and that the transfer between the flavin and the second substrate is mainly affected. Zn-ferrocyanide interacts with the reductase, probably increasing the accessibility of the prosthetic group to the solvent. Ferredoxin reduction was also inhibited by Zn-ferrocyanide in a noncompetitive manner, but the observed Ki was about nine times higher than those for the diaphorase reactions. The electron transfer to Anabaena flavodoxin was not affected by Zn-ferrocyanide. Binding of the apoflavodoxin to the reductase was sufficient to overcome the inhibition by Zn-ferrocyanide, suggesting that the interaction of FNRs with their proteinaceous electron partners may induce a conformational change in the reductase that alters or completely prevents the inhibitory effect. 相似文献
72.
73.
Augusto C. Franco Angela Haag-Kerwer Britta Herzog Thorsten E. E. Grams Erika Ball Eduardo A. de Mattos Fabio R. Scarano Suzanne Barreto Maria A. Garcia Andre Mantovani Ulrich Lüttge 《Trees - Structure and Function》1996,10(6):359-365
Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO2 fixation rates of 28 mol m-2 s-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (qN) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO2 fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (qA) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of qA throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (Fv/Fm) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in Fv/Fm, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition. 相似文献
74.
Vittorio Moretto Fernando Formaggio Marco Crisma Gian Maria Bonora Claudio Toniolo Ettore Benedetti Antonello Santini Michele Saviano Benedetto Di Blasio Carlo Pedone 《Journal of peptide science》1996,2(1):14-27
A complete series of terminally blocked, monodispersed homo-oligopeptides (to the pentamer level) from the sterically demanding, medium-ring alicyclic Cα,α-disubstituted glycine 1-aminocyclooctane-1-carb oxylic acid (Ac8c), and two Ala/Ac8c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and 1H-NMR. The molecular structures of the amino acid derivative Z-Ac8c-OH, the dipeptide pBrBz- (Ac8c)2-OH and the tripeptide pBrBz-(Ac8c)3-OtBu were assessed in the crystal state by X-ray diffraction. Conformational energy computations were performed on the monopeptide Ac-Ac8c-NHMe. Taken together, the results obtained strongly support the view that the Ac8c residue is an effective β-turn and helix former. A comparison is also made with the conformational preferences of α-aminoisobutyric acid, the prototype of Cα, α-disubstituted glycines, and of the other members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n=3, 5–7) investigated so far. The implications for the use of the Ac8c residue in peptide conformational design are considered. 相似文献
75.
Summary A new sterol biotransforming mutant was isolated from NRRL-B3683 Mycobacterium sp. after nitrosoguanidine mutagenesis. The mutant showed an enhanced ability to biotransform stigmasterol into 17-ketosteroids compared with the parental strain. 相似文献
76.
Eduardo A. Nillni Theodore C. Friedman Roberta B. Todd †Nigel P. Birch Y. Peng Loh Ivor M. D. Jackson 《Journal of neurochemistry》1995,65(6):2462-2472
Abstract: Pro-thyrotropin-releasing hormone (proTRH) is the precursor to thyrotropin-releasing hormone (TRH; pGlu-His-Pro-NH2), the hypothalamic releasing factor that stimulates synthesis and release of thyrotropin from the pituitary gland. Five copies of the TRH progenitor sequence (Gln-His-Pro-Gly) and seven cryptic peptides are formed following posttranslational proteolytic cleavage of the 26-kDa rat proTRH precursor. The endopeptidase(s) responsible for the physiological conversion of proTRH to the TRH progenitor form is currently unknown. We examined the in vitro processing of [3H]leucine-labeled or unlabeled proTRH by partially purified recombinant PC1. Recombinant PC1 processed the 26-kDa TRH precursor by initially cleaving the prohormone after the basic amino acid at either position 153 or 159. Based on the use of our well-established antibodies, we propose that the initial cleavage gave rise to the formation of a 15-kDa N-terminal peptide (preproTRH25–152 or preproTRH25–158) and a 10-kDa C-terminal peptide (preproTRH154–255 or preproTRH160–255). Some initial cleavage occurred after amino acid 108 to generate a 16.5-kDa C-terminal peptide. The 15-kDa N-terminal intermediate was further processed to a 6-kDa peptide (preproTRH25–76 or preproTRH25–82) and a 3.8-kDa peptide (preproTRH83–108), whereas the 10-kDa C-terminal intermediate was processed to a 5.4-kDa peptide (preproTRH206–255). The optimal pH for these cleavages was 5.5. ZnCl2, EDTA, EGTA, and the omission of Ca2+ inhibited the formation of pYE27 (preproTRH25–50), one of the proTRH N-terminal products, by 48, 82, 72, and 45%, respectively. This study provides evidence, for the first time, that recombinant PC 1 enzyme can process proTRH to its predicted peptide intermediates. 相似文献
77.
A Rigal E Bouveret R Lloubes C Lazdunski H Benedetti 《Journal of bacteriology》1997,179(23):7274-7279
TolB is a periplasmic protein of the cell envelope Tol complex. It is partially membrane associated through an interaction with the outer membrane lipoprotein PAL (peptidoglycan-associated lipoprotein), which also belongs to the Tol system. The interaction of TolB with outer membrane porins of Escherichia coli was investigated with a purified TolB derivative harboring a six-histidine tag. TolB interacted with the trimeric porins OmpF, OmpC, PhoE, and LamB but not with their denatured monomeric forms or OmpA. These interactions took place both in the presence and in the absence of lipopolysaccharide. TolA, an inner membrane component of the Tol system, also interacts with the trimeric porins via its central periplasmic domain (R. Dérouiche, M. Gavioli, H. Bénédetti, A. Prilipov, C. Lazdunski, and R. Lloubès, EMBO J. 15:6408-6415, 1996). In the presence of the purified central domain of TolA (TolAIIHis), the TolB-porin complexes disappeared to form TolAIIHis-porin complexes. These results suggest that the interactions of TolA and TolB with porins might take place in vivo and might be concomitant events participating in porin assembly. They also suggest that the Tol system as a whole may be involved in porin assembly in the outer membrane. 相似文献
78.
Rebello Celso M.; Ikegami Machiko; Ervin M. Gore; Polk Daniel H.; Jobe Alan H. 《Journal of applied physiology》1997,83(1):213-218
Rebello, Celso M., Machiko Ikegami, M. Gore Ervin, Daniel H. Polk, and Alan H. Jobe. Postnatal lung function and protein permeability after fetal or maternal corticosteroids in preterm lambs.J. Appl. Physiol. 83(1): 213-218, 1997.We evaluated postnatal lung function andintravascular albumin loss to tissues of 123-days-gestation pretermsurfactant-treated and ventilated lambs 15 h after direct fetal(n = 8) or maternal(n = 9) betamethasone treatment orsaline placebo (n = 9). Thebetamethasone-treated groups had similar increases in dynamiccompliances, ventilatory efficiency indexes, and lung volumes relativeto controls (P < 0.05). The lossesof 125I-labeled albumin fromblood, a marker of intravascular integrity, and the recoveries of125I-albumin in muscle and brainwere similar for control and betamethasone-exposed lambs.Betamethasone-treated lambs had lower recoveries of125I-albumin in lung tissues andin alveolar washes than did controls (P < 0.01). Although blood pressureswere higher for the treated groups (P < 0.05), all groups had similar blood volumes, cardiac outputs, andorgan blood flows. Maternal or fetal treatment with betamethasone 15 hbefore preterm delivery equivalently improved postnatal lung function,reduced albumin recoveries in lungs, and increased blood pressures.However, prenatal betamethasone had no effects on the systemicintravascular losses of albumin or did not change blood volumes. 相似文献
79.
Eduardo A. Moscone Josef Loidl Friedrich Ehrendorfer Armando T. Hunziker 《American journal of botany》1995,82(2):276-287
Nucleolar activity of 22 samples belonging to nine diploid species of Capsicum was analyzed in somatic metaphases and interphase nuclei. They are: C, chacoënse, C. parvifolium, C. frutescens, C. chinense, C. annuum var. annuum, C. baccatum var. pendulum, C. pubescens, all with 2n = 24, and C. mirabile var. mirabile and C. campylopodium with 2n = 26. Silver staining was applied for the first time in Capsicum, providing useful markers for chromosome identification in combination with other banding techniques already employed in the genus. From two to eight AgNORs (silver-stained nucleolus organizing regions) were found in the diploid complement of the taxa studied. Nucleolar organizers are located at secondary constrictions of chromosomes which are conventionally stained or banded (C-banding or fluorochrome banding). Polymorphism of AgNORs and attached satellites often occurs. Nucleoli are usually fused to a variable extent. Number and position of active rDNA loci are variable not only between but also within species and populations. Homologies in position of NORs between species were established. The data obtained are related to previous conclusions on phylogenetic relationships in Capsicum. Possible trends of karyotype evolution concerning nucleolar organizers are discussed, and four NORs in the diploid complement (on chromosome pairs #1 [m] and #12 [st]) are regarded as the plesiomorphic condition. 相似文献
80.
Marcelle Bergeron Margaret S. Swain Eduardo Molina-Holgado Tomás A. Reader Roger F. Butterworth 《Neurochemical research》1995,20(8):963-967
Portal-systemic encephalopathy (PSE) is characterized by a neuropsychiatric disorder progressing through personality changes, to stupor and coma. Previous studies have revealed alterations of serotonin and of its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in brain tissue and CSF in experimental (rat) and human PSE. Increased brain 5-HIAA concentrations could result from its decreased removal rather than to increased serotonin metabolism. In order to evaluate this possibility, CSF 5-HIAA concentrations were measured using an indwelling cisterna magna catheter technique at various times following end-to-side portacaval anastomosis in rats (the most widely used animal model of PSE) treated with probenecid, a competitive inhibitor that blocks the active transport of acid metabolites out of the brain and CSF. Following portacaval anastomosis and probenecid treatment, CSF concentrations of 5-HIAA were increased to a greater extent than in sham-operated controls. When data were expressed as per-cent baseline values, the relative increase of CSF 5-HIAA in portacaval shunted rats following probenecid treatment was not significantly different from sham-operated controls. These findings confirm that increased 5-HIAA in the CNS in experimental PSE results from increased 5HT metabolism or turnover and that the probenecid-sensitive acid metabolite carrier is intact in PSE. 相似文献