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I Contreras

Publications and source records attributed to I Contreras.

At least 37 records · Page 2Linked to original sources
PubMed1994

Mini-Mu technology in Salmonella typhi: isolation of stable MudJ operon fusions by cis complementation.

This paper describes a method to achieve stable MudJ insertions in the Salmonella typhi Ty2 chromosome. The method is a modification of the genetic complementation system described previously for Salmonella typhimurium, which consists in placing the defective transposon (MudJ) near the transposase genes of a helper Mu phage on a single DNA fragment. This fragment is then introduced into a new bacterial host by means of P22 transduction. We constructed a S. typhi strain which carries MudJ and the Mu helper phage in the chromosome. This strain was induced to lytic growth and the lysate was used to infect S. typhi Ty2. The frequency of mutation was 2.0 x 10(-6) mutants per recipient bacterium. Superinfection with the Mu helper phage was about 1%. To determine the number of MudJ insertions, several mutants were subjected to Southern blot analysis. From a total of 25 mutants analyzed, only 4 contained more than one insertion. Our procedure compares well with the method described previously for the S. typhimurium-P22 system and can be applied to other Mu sensitive bacteria.

Bacteriophage mu↗
PubMed1992

In chronic uremia, insulin activates receptor kinase but not pyruvate dehydrogenase.

We studied in vivo biochemical effects of insulin in the skeletal muscle of chronically uremic and control rats. The rate of disappearance of blood glucose (determined with a short intravenous test) was reduced by 38% in uremia (p less than 0.05). Intraperitoneal treatment with insulin plus glucose for 30 min caused a 3-fold increase in the activity of insulin receptor tyrosine kinase in the skeletal muscle of both rat groups. Conversely, pyruvate dehydrogenase activity increased by 115% in controls but only by 26% in uremics (p less than 0.01). Exercise (swimming for 30 min) increased muscle pyruvate dehydrogenase activity approximately 2-fold in both groups of animals. These experiments show that in uremic rats, insulin binds normally to its muscle receptors and adequately activates receptor tyrosine kinase but fails to activate an otherwise responsive pyruvate dehydrogenase.

Animals↗
PubMed1990

The effect of fasting on the activation in vivo of the insulin receptor kinase.

Fasting causes insulin resistance in liver and fat, and increases insulin sensitivity in muscle. We studied the response in vitro and in vivo to insulin of the insulin receptor tyrosine kinase in muscle and liver from 72 h fasted and control rats. Insulin was injected intraperitoneally together with glucose, and blood and tissue samples were obtained 0, 5, 15 and 30 min later. Basal serum glucose and insulin levels were significantly higher in control than in fasting rats. Serum glucose rose to approximately 300 mg/dl at 5 min and then progressively declined without hypoglycaemia. Receptors were prepared from whole tissue by wheat germ lectin affinity chromatography. 125I-insulin binding to purified receptors was increased by fasting in both muscle (18%) and liver (50%). In untreated fasting and control animals, muscle and liver insulin receptor tyrosine kinase activity was stimulated to similar levels by insulin added in vitro. With only insulin treatment in vivo, muscle receptor tyrosine kinase behaved similarly in fasting and control animals with maximal activation at 15 min post injection. In liver, insulin in vivo stimulated receptor tyrosine kinase activity maximally at 5 min post injection in both fasting and control, but in fasting animals the treatment in vivo caused a significantly larger and more prolonged activation of the enzymic activity, possibly due to a decrease in the rate of dephosphorylation and deactivation of the beta subunits.

Animals↗
PubMed1990

Effect of a high-fat-sucrose diet on in vivo insulin receptor kinase activation.

Insulin-stimulated glucose uptake into muscle is depressed by high-fat-sucrose (HFS) feeding of rats. To investigate the mechanism of this insulin resistance, the in vivo activation of the insulin receptor kinase in liver and muscle of control and HFS-fed rats was determined. Rats were injected with glucose and insulin and killed 0, 5, 15, and 30 min after injection. Insulin binding was not changed in partially purified receptors from muscle of HFS rats. In control rats insulin receptor kinase activity was maximally stimulated threefold in liver at 5 min and fourfold in muscle at 15 min after insulin-glucose injection. The insulin-stimulated tyrosine kinase activity of receptors isolated from the liver of rats fed the HFS diet was decreased by 30% in comparison with the controls. In contrast, receptors isolated from muscle did not show any difference in basal or insulin-stimulated kinase activity between HFS-fed and control rats. Decreased in vivo activation of the insulin receptor kinase may be at least partially responsible for insulin resistance in liver. Because insulin binding and insulin stimulation of receptor kinase were normal in muscle of HFS-fed animals, it is concluded that the insulin resistance of glucose uptake into muscle is caused by a defect distal to the insulin receptor.

Animals↗
PubMed1987

[Isolation of a cellulase hyperproducer Trichoderma pseudokoningii mutant].

The present study describes the production of cellulases by a native strain of Trichoderma pseudokoningii in the presence and absence of a catabolic repressor. We report a plate assay for selecting fungal mutants capable of synthesizing the cellulase enzymes under conditions of catabolite repression. This method was used for the selection of catabolite repression-resistant mutants. One mutant, B-1, secreted 3.3 times the extracellular protein and 3 times the endoglucanase and filter paper activity in submerged cultures when compared with the wild type strain. The cellobiase activity remained at similar levels in both strains. Although this mutant was isolated as i cellulase producer in the presence of 500 mM glycerol on agar plates, in liquid medium containing the repressor B-1 it exhibits only partial derepression of the cellulase complex.

Cellobiose↗
PubMed1980

[Chemical evaluation of morro or jícaro (Crescentia alata) flours prepared by ensilaging and/or dehydration].

The chemical composition, nutritive value and potential use of the morro fruit (Crescentia alata) has received little attention. The purpose of the present study was: a) to determine appropriate conditions for processing and conservation of the morro fruit without hulls, since a significant part of the production is lost due to inadequate storage conditions, and b) to evaluate, by means of chemical analysis, the whole fruit and its products. For the preparation of dehydrated meals, the content of the fruit was subjected to sun drying and tray drying dehydration with two air temperatures, 60 degrees and 90 degrees C. The method used for the storage of the whole fruit was anaerobic fermentation achieved by ensilaging the fruit in small concrete experimental silos for 90, 145 and 180 days. At the end of each period, the silos were opened. The ensilaged material was of very good appearance and apparently free from unfavorable contaminations; it was dehydrated in tray dryers at an air temperature of 60 degrees C. Independent of processing, the chemical analysis showed the meals to contain on the average 17% crude fat, 11% crude fiber and 18% crude protein. From the amino acid content and using the 1973 FAO/WHO scoring pattern it was found that such flours were limiting in their sulfur amino acid, lysine and threonine content in the order.

Amino Acids↗
PubMed1979

Caulobacter cresentus mutant defective in membrane phospholipid synthesis.

To study the relationship between phospholipid synthesis and organelle biogenesis in the dimorphic bacterium Caulobacter crescentus, auxotrophs have been isolated which require exogenous glycerol or glycerol 3-phosphate for growth when glucose is used as the carbon source. Upon glycerol deprivation, net phospholipid synthesis ceased immediately in a glycerol 3-phosphate auxotroph which was shown to have levels of biosynthetic sn-glycerol 3-phosphate dehydrogenase (E.C. 1.1.1.8) activity 10 times lower than that of the wild type. In the absence of glycerol, the optical density of the culture continued to increase for the equivalent of one generation, although the cells did not divide. After the equivalent of one generation time, rapid cell death occurred. Cell death also occurred when phospholipid synthesis was inhibited by cerulenin. Although ribonucleic acid and protein syntheses continued at a reduced rate for the equivalent of one generation in mutant strains, a substantial decrease in the rate of deoxyribonucleic acid synthesis occurred immediately upon glycerol deprivation. Revertant strains had wild-type levels of glycerol 3-phosphate dehydrogenase activity and normal rates of phospholipid and macromolecular synthesis.

Bacteria↗
PubMed1978

Galactose catabolism in Caulobacter crescentus.

Caulobacter crescentus wild-type strain CB13 is unable to utilize galactose as the sole carbon source unless derivatives of cyclic AMP are present. Spontaneous mutants have been isolated which are able to grow on galactose in the absence of exogenous cyclic nucleotides. These mutants and the wild-type strain were used to determine the pathway of galactose catabolism in this organism. It is shown here that C. crescentus catabolizes galactose by the Entner-Duodoroff pathway. Galactose is initially converted to galactonate by galactose dehydrogenase and then 2-keto-3-deoxy-6-phosphogalactonate aldolase catalyzes the hydrolysis of 2-keto-3-deoxy-6-phosphogalactonic acid to yield triose phosphate and pyruvate. Two enzymes of galactose catabolism, galactose dehydrogenase and 2-keto-3-deoxy-6-phosphogalactonate aldolase, were shown to be inducible and independently regulated. Furthermore, galactose uptake was observed to be regulated independently of the galactose catabolic enzymes.

Aldehyde-Lyases↗
PubMed1978

Membrane phospholipid composition of Caulobacter crescentus.

The phospholipid composition of Caulobacter crescentus CB13 and CB15 was determined. The acidic phospholipids, phosphatidylglycerol and cardiolipin, comprise approximately 87% of the total phospholipids. Neither phosphatidylethanolamine nor its precursor phosphatidylserine was detected. The outer and inner membranes of C. crescentus CB13 were separated, and phospholipid analysis revealed heterogeneity with respect to the relative amounts of phosphatidylglycerol and cardiolipin in the two membranes. As has been shown to be the case for other bacterial membranes, the concentration of cardiolipin increases and phosphatidylglycerol decreases as cell cultures enter stationary phase.

Bacteria↗
PubMed1977

Prevention of vitamin A deficiency by fortification of sugar. A field study.

The small amount of vitamin A in the diet of people living in some regions of Chile can be increased by adding this vitamin to sugar. In order to evaluate the effectiveness of a sugar fortification program, vitamin A fortified sugar was distributed to four indian villages in the mountainous region of Africa, whose inhabitants showed a severe vitamin A deficiency. The results of this study demonstrate that sugar fortification program is able to correct vitamin A deficiency by elevating the vitamin intake and consequently improve the circulating retinol, without substantially increasing the cost or modigying the organoleptic characteristics of sugar.

Carbohydrates↗