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At least 721 records · Page 40Linked to original sources
PubMed1980

Effects of inorganic phosphate on the photosynthetic carbon reduction cycle in extracts from the stroma of pea chloroplasts.

1. Turnover of the photosynthetic carbon reduction cycle has been demonstrated in chlorophyll-free reaction mixtures containing chloroplast stromal extract, as evidenced by the fixation of CO2 following addition of small amounts of 3-phosphoglycerate. 2. The activity of the photosynthetic carbon reduction cycle in this system is inhibited by inorganic phosphate (Pi), with activity reduced to 50% by about 6.5 mM Pi. Pi also increased the lag period which elapsed before a steady rate of CO2 fixation was obtained. 3. The effect of Pi on the rate of 3-phosphoglycerate reduction following the addition of substrate amounts of some cycle intermediates was investigated. Substantial inhibition was observed with fructose 1,6-bisphosphate, sedoheptulose 1,7-bisphosphate and erythrose 4-phosphate as substrates. Pi also affected the activity of ribulose-bisphosphate carboxylase, with stimulation at Pi concentrations below 2.5 mM and inhibition at higher concentrations. 4. The results showed that the sedoheptulose bisphosphatase reaction is inhibited more strongly by Pi than the fructose bisphosphatase reaction. 5. It is concluded that the previously established inhibitory effects of Pi on photosynthesis by intact isolated chloroplasts may be partly due to these inhibitory effects of Pi on the reactions of the photosynthetic carbon reduction cycle.

Carbon Dioxide↗
PubMed2004

Preparation and characterization of thick-film Ni/MH battery.

Using the porous polypropylene (PP) films sputtered with gold and the Ni as current collectors, the electroactive materials (Ni(OH)2 and metal hydride (MH)) of positive and negative electrodes were prepared on the current collector using thick-film technology. Two types of cell configurations were prepared and the characteristics of these batteries were compared. The cycle number for the formation of batteries based on the porous PP film was found to be 2, which was significantly less than that of batteries based on the ceramic substrates. Using the porous PP film as substrate, the number of cycles for the formation of battery increased from 2 to 5 with the increase of the charge/discharge rate from 0.1C/0.025C to 2.0C/0.5C. The silver oxides dendrites formed by the oxidation of silver paste used to adhere the current collectors and the conducting wires in the charge/discharge process caused a short contact between the positive and negative electrodes, which then caused the battery failure. The cycle life of the battery based on the porous PP film was found to be greater than 400 when the charge/discharge rate was 2.0C/0.5C.

Coated Materials, Biocompatible↗
PubMed1982

Substrate-selective maintenance of tissue K+ in perfused rat kidney.

We sought to determine in the functioning, substrate-limited, isolated perfused rat kidney whether there is substrate selectivity for maintenance of renal tissue K+ content (mueq/g dry wt). The kidney was perfused for 75 min with 6 g/100 ml substrate-free albumin in Krebs-Ringer bicarbonate (pH approximately 7.4) in the absence of exogenous substrate (control) or in the presence of one substrate (usually 5 mM) chosen from three groups of substrates: 1) substrates of the glycolytic pathway: glucose, fructose, and glycerol; 2) precursors of or substrates of the tricarboxylic acid cycle: citrate (2 mM), alpha-ketoglutarate, succinate, glutamine, glutamate, and acetate; 3) substrates selectively used by the kidney for synthetic work: glycine and inositol. A significant loss of tissue K+ occurred during perfusion in the absence of exogenous substrate (-17%) and also during perfusion with inositol, glycine, acetate, glutamine, or glycerol. No loss of tissue K+ occurred in the presence of fructose, citrate, alpha-ketoglutarate, succinate, or glutamate. Glucose was unique in that at 10 mM, but not at 5 mM, a loss of tissue K+ occurred. We conclude that there is substrate-selective support of renal tissue K+ content, and that those substrates known to enter principally into energy-requiring biosynthetic pathways do not maintain tissue K+ content.

Animals↗
PubMed1999

Fibronectin substrate induces shortening of in vitro neural crest cell mitotic cycle.

Neural crest cells (NCC) segregate from neural folds, swim through extracellular matrix, and differentiate in several cell types. During in vivo and in vitro dispersion, NCC display a substantial proliferative rate. Here, we have evaluated this biological behavior under the influence of different substrates. NCC exhibit the highest proliferative activity on fibronectin substrate, with shortening of the G1 period. This fact is reverted by specific antibody pre-treatment of the substrate. Taking into account that NCC migrate along narrow and restricted pathways rich in essential fibronectin, with high proliferative rates, these results indicate that the fibronectin pathway contributes to increase the cell number, leading to a high population pressure that could participate in the early dispersion of NCC.

Animals↗
PubMed1994

A method for inducing equi-biaxial and uniform strains in elastomeric membranes used as cell substrates.

A device is described which is designed to bring about uniform and equi-biaxial strains of 0.04-0.4% on a circular elastomeric sheet upon which cells are grown in a monolayer. Strain measurements at six different radii of the well provide evidence of the uniformity of the strain field over the 2.54 cm diameter of the well with a mean strain of 0.15% and a standard deviation of 0.01% strain. Major advantages of the system over those previously described are that (1) the substrate remains in the same plane throughout the application of stretch, (2) the device is designed to provide a state of uniform equi-biaxial strain to the entire substrate of the cells and (3) all cells 'see' the same strain field, no matter what their orientation. This allows for real-time optical monitoring of the cells throughout the stretching cycle of the cell substrate. In this way, changes in the cell membrane, cell nucleus, cytoskeleton and in fluorescently labelled calcium can be monitored microscopically during application of an equi-biaxial mechanical stretch.

Biocompatible Materials↗
PubMed2005

Rapid and highly sensitive electrochemical determination of alkaline phosphatase using a composite tyrosinase biosensor.

The use of an amperometric graphite-Teflon composite tyrosinase biosensor for the rapid monitoring of alkaline phosphatase (ALP), with no need of an incubation step and using phenyl phosphate as the substrate, is reported. Phenol generated by the action of ALP is monitored at the tyrosinase composite electrode through the electrochemical reduction of the o-quinone produced to catechol, which produces a cycle between the tyrosinase substrate and the electroactive product, giving rise to the amplification of the biosensor response and to the sensitive detection of ALP. The current was measured at -0.10 V 5 min after the addition of ALP. As a compromise between high ALP activity and high sensitivity for the detection of phenol, a pH of 8.5 was chosen. The substrate concentration was also optimized. A linear calibration plot was obtained for ALP between 2.0 x 10(-13) and 2.5 x 10(-11), with a detection limit of 6.7 x 10(-14) M. Different types of milk were analyzed with good results, using an extremely simple and rapid procedure.

Agaricales↗
PubMedDate not supplied

Molecular basis for interactions of the DnaK chaperone with substrates.

Hsp70 chaperones assist a large variety of protein folding processes in the cell by transient association with short peptide segments of proteins. The substrate binding and release cycle is driven by the switching between the low affinity ATP bound state and the high affinity ADP bound state of Hsp70. Considerable progress has been made recently by the identification of in vivo substrates for the Escherichia coli homolog, DnaK, and the molecular mechanisms which govern the DnaK-substrate interactions. Here we review the processes that generate DnaK substrates in vivo and the properties of these substrates, and we describe insights gained from structural and kinetic analysis of DnaK-substrate interaction.

Animals↗
PubMed1988

Fluorophore-labeled ether lipids: substrates for enzymes of the platelet-activating factor cycle in peritoneal polymorphonuclear leukocytes.

Cell-free preparations of ionophore-stimulated peritoneal rat polymorphonuclear neutrophils (PMNs) incubated with 1-(N-dansyl-11-amino-1-undecyl)-sn-glycerol-3-phosphorylcholine (dansyllyso-PAF) converted this fluorescent lyso ether lipid into two different classes of products. In the absence of acetyl-CoA 1-(N-dansyl-11-amino-1-undecyl)-2-long chain acyl-sn-glycerol-3-phosphorylcholine (dansylalkyl-2-acyl-GPC) was the only identified new fluorescent phospholipid. In the presence of acetyl-CoA an additional new product, 1-(N-dansyl-11-amino-1-undecyl)-2-acetyl-sn-glycerol-3-phosphorylcholine (dansyl-PAF), was formed. The formation of dansyl-PAF in PMN homogenates was only transient with a maximum after about 4 min. When PMN homogenates were incubated with dansyl-PAF the formation of dansyllyso-PAF was observed prior to the formation of dansyl-2-acyl-GPC. Thus, our data indicate that enzymatically formed dansyl-PAF is completely remodeled into dansylalkyl-2-acyl-GPC by the sequential action of PAF acetylhydrolase and CoA-independent transacylase. These results demonstrate that peritoneal rat PMNs contain lyso-PAF acetyltransferase, PAF acetylhydrolase, and CoA-independent transacylase and that fluorophore-labeled ether lipids provide an easy means to assay enzymes which catalyze important enzymatic reactions involved in the biosynthesis and remodeling of platelet-activating factor.

Animals↗
PubMed2001

Putative helix F contributes to regioselectivity of hydroxylation in mitochondrial cytochrome P450 27A1.

On the basis of alignment with structurally characterized cytochromes P450 (P450s), we have identified the putative F and G helices of mitochondrial P450s 27A1 and 11A. We introduced substitutions at Phe-207, Ile-211, and Phe-215 within putative helix F and at Trp-235 and Tyr-238 within putative helix G in P450 27A1 and compared wild type and mutants with respect to catalytic activity, product pattern, substrate binding, formation of hydrogen peroxide, and interaction with redox partner. Results indicate that the mutated residues are important for delivery of the correctly oriented substrate to the P450 active site. The I211K and F215K mutations, for example, affected the regioselectivity of P450 27A1-dependent hydroxylation reactions and conferred the P450 capacity to cleave the C-C bond of the substrate during the catalytic cycle. Studies of P450 11A1 indicate that Phe-202 has functions similar to those of its counterpart in P450 27A1 (Phe-215). We propose that putative helices F and G form the sides of the substrate-access channel, thus providing the additional mechanism to control regioselectivity of hydroxylation in mitochondrial P450s.

Amino Acid Sequence↗
PubMed2002

Mammalian Orc1 protein is selectively released from chromatin and ubiquitinated during the S-to-M transition in the cell division cycle.

Previous studies have shown that changes in the affinity of the hamster Orc1 protein for chromatin during the M-to-G(1) transition correlate with the activity of hamster origin recognition complexes (ORCs) and the appearance of prereplication complexes at specific sites. Here we show that Orc1 is selectively released from chromatin as cells enter S phase, converted into a mono- or diubiquitinated form, and then deubiquitinated and re-bound to chromatin during the M-to-G(1) transition. Orc1 is degraded by the 26S proteasome only when released into the cytosol, and peptide additions to Orc1 make it hypersensitive to polyubiquitination. In contrast, Orc2 remains tightly bound to chromatin throughout the cell cycle and is not a substrate for ubiquitination. Since the concentration of Orc1 remains constant throughout the cell cycle, and its half-life in vivo is the same as that of Orc2, ubiquitination of non-chromatin-bound Orc1 presumably facilitates the inactivation of ORCs by sequestering Orc1 during S phase. Thus, in contrast to yeast (Saccharomyces cerevisiae and Schizosaccharomyces pombe), mammalian ORC activity appears to be regulated during each cell cycle through selective dissociation and reassociation of Orc1 from chromatin-bound ORCs.

Animals↗
PubMed1997

FIN13, a novel growth factor-inducible serine-threonine phosphatase which can inhibit cell cycle progression.

We have identified a novel type 2C serine-threonine phosphatase, FIN13, whose expression is induced by fibroblast growth factor 4 and serum in late G1 phase. The protein encoded by FIN13 cDNA includes N- and C-terminal domains with significant homologies to type 2C phosphatases, a domain homologous to collagen, and an acidic domain. FIN13 expression predominates in proliferating tissues. Bacterially expressed FIN13 and FIN13 expressed in mammalian cells exhibit serine-threonine phosphatase activity, which requires Mn2+ and is insensitive to inhibition by okadaic acid. FIN13 is localized in the nuclei of transiently transfected cells. Cotransfection of FIN13-expressing plasmids with a plasmid that expresses the neomycin resistance gene inhibits the growth of drug-resistant colonies in NIH 3T3, HeLa and Rat-1 cells. In transiently transfected cells, FIN13 inhibits DNA synthesis and results in the accumulation of cells in G1 and early S phases. Similarly, the induction of expression of FIN13 under the control of a tetracycline-regulated promoter in NIH 3T3 cells leads to growth inhibition, with accumulation of cells in G1 and early S phases. Thus, overexpression and/or unregulated expression of FIN13 inhibits cell cycle progression, indicating that the physiological role of this phosphatase may be that of regulating the orderly progression of cells through the mitotic cycle by dephosphorylating specific substrates which are important for cell proliferation.

3T3 Cells↗
PubMed1993

Controlling the regiospecificity and coupling of cytochrome P450cam: T185F mutant increases coupling and abolishes 3-hydroxynorcamphor product.

Cytochrome P450cam (P450CIA1) catalyzes the hydroxylation of camphor and several substrate analogues such as norcamphor and 1-methyl-norcamphor. Hydroxylation was found experimentally at the 3, 5, and 6 positions of norcamphor, but only at the 5 and 6 positions of 1-methyl-norcamphor. In the catalytic cycle, the hydroxylation of substrate is coupled to the consumption of NADH. For camphor, the degree of coupling is 100%, but for both norcamphor and 1-methyl-norcamphor, the efficiency is dramatically lowered to 12% and 50%, respectively. Based on an examination of the active site of P450cam, it appeared that mutating position 185 might dramatically alter the product specificity and coupling of hydroxylation of norcamphor by P450cam. Analysis of molecular dynamics trajectories of norcamphor bound to the T185F mutant of cytochrome P450cam predicted that hydroxylation at the 3 position should be abolished and that the coupling should be dramatically increased. This mutant was constructed and the product profile and coupling experimentally determined. The coupling was doubled, and hydroxylation at the 3 position was essentially abolished. Both of these results are in agreement with the prediction.

Binding Sites↗
PubMed1995

Localization and activity of adrenal carbonyl reductase during the estrous cycle.

Changes in carbonyl reductase (CR) activity towards seven substrates in adrenal glands of female rats were investigated during estrous cycle and the circadian patterns of adrenal CR activity towards seven substrates in male rats were examined. The localization of the enzyme protein in the adrenal gland was carried out by immunohistochemistry. In female rats, adrenal CR activity was lowest between 1200 and 2000 h on the day of proestrus, the phase in which a large, significant increase in ovarian steroids, gonadotropins and prolactin is observed. Immunoreactivity in the zona reticularis of the adrenal cortex to anti-adrenal CR, CR-K2, antibody on the day of proestrus was faint or negative compared with that on other days of the estrous cycle. In male rats, no major changes in adrenal CR activity were observed compared with females, although these were slight changes in all the enzyme activities. These results suggest that adrenal CR may be negatively regulated by the pituitary-adrenal axis in female rats and, in particular, on the day of proestrus.

Adrenal Glands↗
PubMed1991

Performance and metabolic responses to a high caffeine dose during prolonged exercise.

The present study examined whether a high caffeine dose improved running and cycling performance and altered substrate metabolism in well-trained runners. Seven trained competitive runners [maximal O2 uptake (VO2max) 72.6 +/- 1.5 ml.kg-1.min-1] completed four randomized and double-blind exercise trials at approximately 85% VO2max; two trials running to exhaustion and two trials cycling to exhaustion. Subjects ingested either placebo (PL, 9 mg/kg dextrose) or caffeine (CAF, 9 mg/kg) 1 h before exercise. Endurance times were increased (P less than 0.05) after CAF ingestion during running (PL 49.2 +/- 7.2 min, CAF 71.0 +/- 11.0 min) and cycling (PL 39.2 +/- 6.5 min, CAF 59.3 +/- 9.9 min). Plasma epinephrine concentration [EPI] was increased (P less than 0.05) with CAF before running (0.22 +/- 0.02 vs. 0.44 +/- 0.08 nM) and cycling (0.31 +/- 0.06 vs. 0.45 +/- 0.06 nM). CAF ingestion also increased [EPI] (P less than 0.05) during exercise; PL and CAF values at 15 min were 1.23 +/- 0.13 and 2.51 +/- 0.33 nM for running and 1.24 +/- 0.24 and 2.53 +/- 0.32 nM for cycling. Similar results were obtained at exhaustion. Plasma norepinephrine was unaffected by CAF at rest and during exercise. CAF ingestion also had no effect on respiratory exchange ratio or plasma free fatty acid data at rest or during exercise. Plasma glycerol was elevated (P less than 0.05) by CAF before exercise and at 15 min and exhaustion during running but only at exhaustion during cycling. Urinary [CAF] increased to 8.7 +/- 1.2 and 10.0 +/- 0.8 micrograms/ml after the running and cycling trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

[Mechanism of ischemic disorders of fatty acid oxidation in heart mitochondria].

The article deals with the effect of permanent, temporal and total myocardial ischemia on the oxidation of acetate, hexanoate, palmitoylcarnitine and palmitoyl-CoA in isolated rabbit heart mitochondria. All the three models of ischemia in different experimental situations demonstrated a similar degree of fatty acid oxidation suppression independent of the length of acyl residue, the suppression being the greatest during the first hours and in total ischemia. Both in the control and in ischemia, respiratory activity was at its highest level with acetate, decreasing in the order above. Thus, the rate of Krebs' cycle reactions and of respiratory chain does not limit medium- and long-chain fatty acid oxidation. It is nevertheless established that suppression of their oxidation in ischemia is completely determined by the decrease of cytochrome S and of endogenous substrate intermediates of Krebs' cycle in the mitochondria; decreased adenine nucleotide and carnitine-palmitoyl-transferase transport (other authors' data) is not critical, at least in early ischemia (0.5 h). Ischemic mitochondria are characterized by incomplete palmitoylcarnitine oxidation.

Acetates↗
PubMed1978

Growth inhibition of transformed cells with succinylated concanavalin A.

Succinylated concanavalin A reversibly inhibits the growth of SV40 transformed mouse 3T3 cells and thus causes an accumulation of the cells in the G1 phase of the cell cycle. In a soft substrate (methylcellulose) succinylated concanavalin A also restores in transformed cells the growth behavior typical of untransformed cells.

Cell Adhesion↗