Intersiembra maíz - soja : variación espacial y temporal de propiedades del suelo

p.43-52La dinámica de los nutrientes y otras propiedades del suelo pueden ser alteradas fuertemente por prácticas agrícolas como la intersiembra. Se propusieron los siguientes objetivos: I) comparar sistemas de intersiembra soja-maíz con respecto a los monocultivos en cuanto a la cantidad de carbono del suelo, II) evaluar la disponibilidad de los principales nutrientes en estos sistemas. Se realizó un ensayo en un suelo Hapludol típico de la Pampa Arenosa con los siguientes tratamientos: I) soja pura, II) maíz puro y III) soja y maíz intersembrados en una relación 2:1, todos manejados en secano. Se realizaron muestreos de suelo en dos momentos: el primero (F1) se realizó con el maíz en V5 y la soja recién emergida; el segundo (F2) con el cultivo de maíz en R1 y el cultivo de soja en bajo los tratamientos que incluían al cultivo de maíz. El nivel de P extractable fue menor en el cultivo de soja avanzado (F2) que en el monocultivo de maíz, lo que fue notable a 5 cm del surco, debido probablemente a una fuerte absorción por parte de la leguminosa. En la primera fecha de medición, a 5 cm del surco correspondiente, que incluían al maíz, mientras que en la segunda fecha de medición, la disponibilidad de nitratos fue mínima en dicho tratamiento, lo que parece deberse a diferencias en el desarrollo de los cultivos. Por último, la práctica de intersiembra dentro del marco de este ensayo no probó ser una alternativa viable para limitar la existencia de elevados niveles de nitratos

The Elusive Third Subunit IIa of the Bacterial B-Type Oxidases: The Enzyme from the Hyperthermophile Aquifex aeolicus

The reduction of molecular oxygen to water is catalyzed by complicated membrane-bound metallo-enzymes containing variable numbers of subunits, called cytochrome c oxidases or quinol oxidases. We previously described the cytochrome c oxidase II from the hyperthermophilic bacterium Aquifex aeolicus as a ba3-type two-subunit (subunits I and II) enzyme and showed that it is included in a supercomplex involved in the sulfide-oxygen respiration pathway. It belongs to the B-family of the heme-copper oxidases, enzymes that are far less studied than the ones from family A. Here, we describe the presence in this enzyme of an additional transmembrane helix “subunit IIa”, which is composed of 41 amino acid residues with a measured molecular mass of 5105 Da. Moreover, we show that subunit II, as expected, is in fact longer than the originally annotated protein (from the genome) and contains a transmembrane domain. Using Aquifex aeolicus genomic sequence analyses, N-terminal sequencing, peptide mass fingerprinting and mass spectrometry analysis on entire subunits, we conclude that the B-type enzyme from this bacterium is a three-subunit complex. It is composed of subunit I (encoded by coxA2) of 59000 Da, subunit II (encoded by coxB2) of 16700 Da and subunit IIa which contain 12, 1 and 1 transmembrane helices respectively. A structural model indicates that the structural organization of the complex strongly resembles that of the ba3 cytochrome c oxidase from the bacterium Thermus thermophilus, the IIa helical subunit being structurally the lacking N-terminal transmembrane helix of subunit II present in the A-type oxidases. Analysis of the genomic context of genes encoding oxidases indicates that this third subunit is present in many of the bacterial oxidases from B-family, enzymes that have been described as two-subunit complexes

Tyrosinaemia type Ia without excess of urinary succinylacetone

Tyrosinaemia type I (McKusick 276700) (Kvittingen 1991) is an autosomal recessively inherited metabolic disorder due to two enzymatic deficiencies: fumarylacetoacetase (FAH) (type Ia) and maleylacetoacetate isomerase (type Ib) (Berger et al 1988). Elevation of urinary succinylacetone (SA) is usually deemed to be specific for tyrosinaemia type I. Diagnosis is made by assessing plasma tyrosine levels and urinary SA and by determining the activity of FAH in fibroblasts or lymphocytes. We report the case of a 3-year-old female child affected by tyrosinaemia type Ia, with persistent low levels of plasma tyrosine and no excess of urinary SA. Maria M. was born to first-degree cousins; the postnatal period is reported as uneventful. At 7 months of age hepatomegaly was noted and the child was hospitalized. At that time plasma tyrosine was slightly elevated (425 #mol/L by ion exchange chromatography), with moderate tyrosinuria. No excess of SA was detectable in urine by GC-MS. c~-Fetoprotein serum level was > 300 IU/ml. Liver ultrasound and CT scans showed hepatomegaly and multifocal micronodular structural abnormalities. Tyrosinaemia type I was then suspected despite the absence of SA and a dietary regimen with low phenylalanine and tyrosine intake (25mg/kg per day) wasintroduced. One month later, plasma tyrosine level was in the normal range (100/~mol/L). The clinical picture has always been good, including adequate psychomotor development, except for a marked hepatomegaly (4 cm below the costal arch); plasma tyrosine was steadily below l l0/tmol/L with only a slight elevation of plasma methionine; a major biochemical abnormality was c~-fetoprotein 4232 IU/ml (normal 0.01-7.00). On the basis of the good metabolic control, diet was then progressively relaxed in order to assess her dietary tyrosine tolerance (up to 100mg/kg per day). Plasma tyrosine levels remained constantly below 160 #mol/L, even 3 h after a meal. Urinary SA was still absent. Tyrosinaemia was then monitored for 1 year on a relaxed diet, being continuously below l l0#mol/L even after a protein load test providing 100mg/kg body weight, with no detectable urinary SA and only slight increase of 6-aminolaevulinic acid (600 ~mol/L; normal < 500/~mol/L). Hepatomegaly was the only clinical abnormality ever reported. The child stayed on a relaxed diet until the diagnosis of tyrosinaemia type Ia was confirmed by enzymatic activity determination on cultured skin fibroblasts (FAH 0.19nmol/min per mg protein; normal 0.67) performed at Professor R. Berger's Metabolic Laboratory, Wilhelmina Kinderziekenhuis, Utrecht. In the meantime her younger sister, aged 2 months, was admitted to another centre for recurrent vomiting, diarrhoea and jaundice. She had hepatomegaly (4 cm below costal arch) and elevation of serum total and conjugated bilirubin, ammonia, AST and ALT. Plasma tyrosine was 510#mol/L. In 24h her clinical picture worsened acutely with occurrence of seizures, dyspnoea, cyanosis and haematemesis, until death. Post-mortem liver histology showed a diffuse cirrhosis and features suggestive of tyrosinaemia type I. Maria was referred again to our department for progressive restriction of the dietary tyrosine intake. At that time liver ultrasound scan showed no modification of the previous picture of cirrhosis. Serum c~-fetoprotein level was 795 IU/ml. Three months later she remained in very good clinical condition, with adequate psychomotor development; plasma tyrosine was 70#mol/L and urinary SA still present in undetectable or trace amounts. We report this case of tyrosinaemia type Ia to encourage consideration of this disease even when the biochemical picture is not properly suggestive of it. Furthermore, the family history confirms the possible occurrence of acute and chronic forms of this disease in one family. Also, we believe that it demonstrates that no biochemical parameter by itself is pathognomonic for this disease, and that any slight elevation of plasma tyrosine levels even without SA urinary excess is worth further investigatio

[Thoraco-pulmonary wounds caused by hunting rifles. Treatment and classification]

PMID: 667484