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.     

Aquatic bird densities in two coastal lagoon systems in Chiapas State,Mexico, a preliminary assessment

Six bodies of water in two coastal lagoon systems were investigated in Chiapas State, Mexico between July, 1990 and February, 1991. The size of water bodies ranged from 102.5 to 847.5 ha. Salinity varied seasonally being the lowest in July during the rainy season (1.0) and highest in February (35.8). The waters are hypertrophic with total phosphorus concentrations as high 900 mg m^–3.The number of bird species was the highest in February (N = 9 to 23) and the lowest in July (N = 2 to 15). The majority of birds present are resident species of Mexico but several species of northern birds were present in February (e.g. Lesser Scoup, Osprey, Peregrin Falcon).The number of birds observed in the waterbodies varied during the study period being as high as 2800 Cormorants, 2300 White Pelicans and 681 Limpkins, at a particular time, or expressed in terms of units surface area of each lagoon 8.0, 2.7 and 1.9 individuals per hectare respectively. The daily food requirements of White Pelicans at such a high density is about 4.1 kg ha^–1 d^–1.The hypertrophic state of Cerritos Lagoon allows a sufficient level of production to support such a high food requirement. Considering the limited survey time spent on the lagoons the bird population numbers are probably underestimated.     

Characterization of the cit-1 gene from Neurospora crassa encoding the mitochondrial form of citrate synthase

We have isolated the cDNA and corresponding genomic DNA encoding citrate synthase in Neurospora crassa. Analysis of the protein coding region of this gene, named cit-1, indicates that it specifies the mitochondrial form of citrate synthase. The predicted protein has 469 amino acids and a molecular mass of 52002 Da. The gene is interrupted by four introns. Hybridization experiments show that a cit-1 probe binds to two different fragments of genomic DNA, which are located on different chromosomes. Neurospora crassa may have two isoforms of citrate synthase, one in the mitochondria and the other in microbodies.     

Effects of decreased atmospheric deposition on the sulfur budgets of two Dutch moorland pools

The chemical composition of surface waters of two Dutch moorland pools and of incident precipitation, was monitored from 1982 to 1990. For this period, sulfur and water budgets were calculated using a hydrochemical model developed for well-mixed non-stratifying lakes. Total atmospheric deposition of S decreased significantly after 1986 at both locations. A model describing the sulfur budget in terms of input, output and reduction/oxidation processes predicted a fast decrease of pool water SO₄ ²⁻ concentrations after a decrease of atmospheric input. However, SO₄ ²⁻ concentrations in the surface water was lowered only slightly or remained constant. Apparently a source within the lake caused the unexpectedly high SO₄ ²⁻ concentrations. The possible supply of SO₄ ²⁻ from the sediment through regulation by (K-)Al-SO₄ containing minerals or desorption of SO₄ ²⁻ from positively charged surfaces in the sediment was evaluated. Solubility calculations of pore water with respect to alunite, basaluminite and jurbanite indicated that SO₄ ²⁻ concentration was not regulated by these minerals. It is suggested here (1) that desorption of SO₄ ²⁻ from peaty sediments may account for the estimated SO₄ ²⁻ supply provided that the adsorption complex is periodically recharged by partial oxidation of the upper bottom sediments and (2) that because of exposure of a part of the pool bottom to the atmosphere during dry summers and subsequent oxidation of reduced S, the amount of SO₄ ²⁻ may be provided which complements the decreasing depositional SO₄ ²⁻ input. In future research these two mechanisms need to be investigated.     

Characterization of the cit-1 gene from Neurospora crassa encoding the mitochondrial form of citrate synthase

We have isolated the cDNA and corresponding genomic DNA encoding citrate synthase in Neurospora crassa. Analysis of the protein coding region of this gene, named cit-1, indicates that it specifies the mitochondrial form of citrate synthase. The predicted protein has 469 amino acids and a molecular mass of 52002 Da. The gene is interrupted by four introns. Hybridization experiments show that a cit-1 probe binds to two different fragments of genomic DNA, which are located on different chromosomes. Neurospora crassa may have two isoforms of citrate synthase, one in the mitochondria and the other in microbodies.     

Molecular modelling of the photoconduction mechanism by charged solitons intrans-polyacetylene: I

It is possible to rationalize the different steps involved in the photoconductivity observed intrans-polyacetylene (t-PA) in terms of a simple chemical model. The interchain electron transfer (IET) and the intrachain polaron capture by neutral solitons proposed by Orensteinat al. may be represented within a simple molecular orbital (MO) picture. An efficiency index for the IET is proposed in terms of the binding energy of the charged polarons and of the electronic chemical potential. The predictive power of the efficiency index is analyzed in the context of the global softness concept. An MO protocol is described to obtain estimates of the IET hopping probabilities.     

Biodiversity of sweetpotato (iPomoea batatas,Convolvulaceae) in Southern Mexico

Between 1987 and 1992 the phytogeographic region of southern Mexico was explored during three collecting trips made in search of cultivated and wild germplasm of the sweetpotato (Ipomoea batatas). The first trip was made in 1987, when we collected wild species in Ipomoea section Batatas found in the southeastern and southwestern regions of Mexico. A second trip was made in 1990, when we collected accessions of the cultivated species as well as wild species in the southeast, southwest and northeast. The third and final trip was oriented at identification, characterization and collecting seeds in the ecological niches ofI.tabascana andI.umbraticola. As a result of the three trips we collected 165 accessions of cultivated and wild germplasm with populations dispersed in 147 localities in 15 states of the Mexican region: Veracruz, Tabasco, Campeche, Chiapas, Oaxaca, Yucatán, Guerrero, Michoacán, San Luis Potosí, Hidalgo, Querétaro, Tamaulipas, Guanajuato, Puebla and México. Of the total accessions some 64 (38.3%) were of the cultivated species including nine accessions of feral material, and 103 accessions (61.7%) were of wild species made up of 59 accessions of seven species in the section Batatas, 37 of other species in the family Convolvulaceae, and seven yet to be determined. We have identified the largest genetic biodiversity in six localities of five states: Tabasco, Oaxaca, Michoacán, San Luis Potosí, and Puebla. Biodiversity maintenance in this region is associated with the day-of-the-dead festivities.     

Temperature coefficients of peptides dissolved in hexafluoroisopropanol monitor distortions of helices

Temperature coefficients are widely used as an indication of solvent accessibility to amide protons. Low temperature coefficients are related to low accessibility and are often interpreted as evidence for intramolecular hydrogen bonding. Conformational shifts, i.e. the difference between chemical shifts of a particular residue in a structured and in a random-coil conformation, provide information on secondary structure. In particular, negative CH conformational shifts are often used to delineate the extent of helical stretches. NH conformational shifts show large oscillations within a helix that have been interpreted as the result of helix distortions affecting hydrogen bond lengths. In the course of the study of different peptides that adopt a helical structure in the presence of the structure-inducing solvent hexafluoroisopropanol (HFIP), we have found a strong correlation between temperature coefficients and amide conformational shifts. However, contrary to the initial expectations, lower temperature coefficients were associated to amide protons involved in longer, and presumably weaker, hydrogen bonds. The correlation can be explained, however, assuming that, in helical peptides dissolved in HFIP, temperature affects the chemical shift of amide protons mainly by changing the average length of intramolecular hydrogen bonds and changes in solvent accessibility play only a secondary role under these experimental conditions. The pattern of temperature coefficients in helical peptides can therefore be used to identify short or long hydrogen bonds causing bending of the helix axis.