Housekeeping genes essential for pantothenate biosynthesis are plasmid-encoded in <Emphasis Type="Italic">Rhizobium etli</Emphasis> and <Emphasis Type="Italic">Rhizobium leguminosarum</Emphasis>

Background  

A traditional concept in bacterial genetics states that housekeeping genes, those involved in basic metabolic functions needed for maintenance of the cell, are encoded in the chromosome, whereas genes required for dealing with challenging environmental conditions are located in plasmids. Exceptions to this rule have emerged from genomic sequence data of bacteria with multipartite genomes. The genome sequence of R. etli CFN42 predicts the presence of panC and panB genes clustered together on the 642 kb plasmid p42f and a second copy of panB on plasmid p42e. They encode putative pantothenate biosynthesis enzymes (pantoate-β-alanine ligase and 3-methyl-2-oxobutanoate hydroxymethyltransferase, respectively). Due to their ubiquitous distribution and relevance in the central metabolism of the cell, these genes are considered part of the core genome; thus, their occurrence in a plasmid is noteworthy. In this study we investigate the contribution of these genes to pantothenate biosynthesis, examine whether their presence in plasmids is a prevalent characteristic of the Rhizobiales with multipartite genomes, and assess the possibility that the panCB genes may have reached plasmids by horizontal gene transfer.     

A cross-flow reactor with immobilized pectolytic enzymes for juice clarification

Summary A new system for continuous juices clarification is presented. The bioreactor combines microporous plates commercially available and industrial pectinases immobilized on nylon membranes in a cross-flow configuration. The kinetic behaviour of the reactor for different recirculation flow rates has been determined. Fresh apricot juice has been continuously clarified in the bioreactor with excellent results.     

24-Methyl-23-dehydrocholesterol: a new sterol intermediate in C-24 demethylation from the nematodes Panagrellus redivivus and Caenorhabditis elegans?

Panagrellus redivivus produced 24-methyl-23-dehydrocholesterol as 4.0% of the 4-desmethylsterols when propagated in a medium containing campesterol as the dietary sterol. The re-examination of previous data revealed that Caenorhabditis elegans produced 1.8% 24-methyl-23-dehydrocholesterol when propagated in medium containing campesterol. 24-Methyl-23-dehydrocholesterol was not detected when the nematodes were propagated in medium containing 22-dihydrobrassicasterol or 24-methylenecholesterol. This may be a result of the greater efficiency of dealkylation of the latter two sterols. This is the first report of the natural occurrence of this sterol in a non-photosynthetic organism, and the first report in organisms that dealkylate 24-alkylsterols.     

Evolutionary history of Na,K-ATPases and their osmoregulatory role

The Na/K pump, or Na,K-ATPase, is a key enzyme to the homeostasis of osmotic pressure, cell volume, and the maintenance of electrochemical gradients. Its α subunit, which holds most of its functions, belongs to a large family of ATPases known as P-type, and to the subfamily IIC, which also includes H,K-ATPases. In this study, we attempt to describe the evolutionary history of IIC ATPases by doing phylogenetic analysis with most of the currently available protein sequences (over 200), and pay special attention to the relationship between their diversity and their osmoregulatory role. We include proteins derived from many completed or ongoing genome projects, many of whose IIC ATPases have not been phylogenetically analyzed previously. We show that the most likely origin of IIC proteins is prokaryotic, and that many of them are present in non-metazoans, such as algae, protozoans or fungi. We also suggest that the pre-metazoan ancestor, represented by the choanoflagellate Monosiga brevicollis, whose genome has been sequenced, presented at least two IIC-type proteins. One of these proteins would have given rise to most current animal IIC ATPases, whereas the other apparently evolved into a lineage that, so far, has only been found in nematodes. We also propose that early deuterostomes presented a single IIC gene, from which all the extant diversity of vertebrate IIC proteins originated by gene and genome duplications. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mitochondrial ATPase inactivation by interaction with its substrate

Purified F₁-ATPase is slowly inactivated by interaction, in a preincubation medium, with its substrate MgATP. Interaction with Mg²⁺ before addition of ATP to the preincubation medium is essential to induce the inactivation. This inactivation is different from other Mg²⁺-induced inhibitions previously described. Free ATP concentration is implicated in the inactivation process and a linear relationship can be established between this concentration and the number of turnovers which are necessary for total inactivation. ITP, 2′-dATP, and GTP can also induce inactivation. Although ITP and GTP are hydrolyzed at a lower rate than ATP and 2′-dATP, they induce inactivation after a smaller number of turnovers than the latter. This process closely follows a kinetics of the type described for suicide enzymes. A reaction scheme is suggested and discussed.     

Histochemistry and histoenzymology of the hydatid cyst (Echinococcus granulosus Batsch, 1786). I. The germinal membrane.

Healthy germinal membranes of hydatid cysts from lungs of human and bovine sources were dissected and isolated for histochemical and histoenzymatic research. These techniques were performed in frozen sections and pieces of the whole membrane. Enzymatic research showed that the germinal membrane presents highly differentiated metabolic areas. These areas were topographically related with the origin and insertion of brood capsules, having differentiated structures for metabolic interchange with scolices. Taking our data into account it may be suggested that this functional differentiation could be transitory and variable for all the membrane surface. The accumulation of lipids and enzymes such as simple estarase, lipase, beta-HDH, alpha-GDH and NADPH-reductase in those areas, suggests that lipids are not a simple excretory product. This distribution probably implies that lipid metabolism or its resultant products are important in development and growth of scolices. In that sense other authors' findings and hypothesis about the possible existence of an endocrine system of the parasite, are considered. This idea being demonstrated in further researches, the lipid metabolic pathways shall bring a good pharmacological approach to the interference with parasite development.