Comparison of cobalamin-independent and cobalamin-dependent methionine synthases from Escherichia coli: two solutions to the same chemical problem.

In Escherichia coli, two enzymes catalyze the synthesis of methionine from homocysteine using methyltetrahydrofolate as the donor of the required methyl group: cobalamin-dependent and cobalamin-independent methionine synthases. Comparison of the mechanisms of these two enzymes offers the opportunity to examine two different solutions to the same chemical problem. We initiated the research described here to determine whether the two enzymes were evolutionarily related by comparing the deduced amino acid sequences of the two proteins. We have determined the nucleotide sequence for the metE gene, encoding the cobalamin-independent methionine synthase. Our results reveal an absence of similarity between the deduced amino acid sequences of the cobalamin-dependent and cobalamin-independent proteins and suggest that the two have arisen by convergent evolution. We have developed a rapid one-step purification of the recombinant cobalamin-independent methionine synthase (MetE) that yields homogeneous protein in high yield for mechanistic and structural studies. In the course of these studies, we identified a highly reactive thiol in MetE that is alkylated by chloromethyl ketones and by iodoacetamide. We demonstrated that alkylation of this residue, shown to be cysteine 726, results in complete loss of activity. While we are unable to deduce the role of cysteine 726 in catalysis at this time, the identification of this reactive residue suggests the possibility that this thiol functions as an intermediate methyl acceptor in catalysis, analogous to the role of cobalamin in the reaction catalyzed by the cobalamin-dependent enzyme.     

The transition point for protein synthesis in late S-G2 may be delayed by genome bromosubstitution without affecting the time of entry into mitosis

Bromosubstitution for most of the S period in synchronous populations of Allium cepa L. meristematic cells resulted in a delay in the late S-G2 transition point where protein synthesis is needed for later mitotic entrance to occur. This retardation in the position of the transition point was not accompanied by the expected delay in the entrance into mitosis, suggesting that such protein synthesis is a requisite, but not a timer for prophase triggering.     

Human enzyme polymorphism in the Canary Islands. III. Tenerife Island population

We analyzed the genetic polymorphism of eight red cell enzymes in samples from different geographical areas of Tenerife and the Iberian peninsula. The gene frequency heterogeneity found within the Tenerife samples was at the same level as that of Tenerife-mainland comparisons. The presence of the Negroid G6PD A+ allele in the Tenerife samples is evidence of an African admixture with a mean estimation of 4.5%.     

Helicobacter pylori in Barrett's esophagus.

Barrett's esophagus is an anatomicoclinical state in which, due to the prolonged action of gastroesophageal reflux, the squamous epithelium is replaced by columnar epithelium. Helicobacter pylori has been implicated in the pathogenesis of various gastrointestinal disorders and has occasionally been observed in Barrett's esophagus. The aim of this study is to determine the incidence of H. pylori in Barrett's esophagus and try to establish its role in the pathogenesis of this disorder. H. pylori was observed in 31 biopsies (44.3%) of the 70 studied, mainly when the epithelium is of the gastric atrophic-fundic type (p less than 0.01). Its presence shows no relation to the degree of inflammatory activity and does not seem, therefore, to play an important role in the pathogenesis of the lesion.     

Metabolic response to ethanol and isopropanol in D. funebris and D. immigrans

Ethanol at low concentration increases larval viability in D. funebris and D. melanogaster and decreases it in D. immigrans. Isopropanol decreases viability in all three species. Isopropanol depresses alcohol dehydrogenase activity. This is accompanied by a change in the relative proportion of electrophoretic forms of the enzyme. Acetone appears in the medium when larvae of D. funebris and D. immigrans develop in the presence of isopropanol. It can be transformed again into isopropanol on reaching a threshold value. It seems that this transformation cannot be carried out by alcohol dehydrogenase alone.     

Phylogenetic relationships in the family Resedaceae L.

A study was made on the phylogenetic relationships of species of the family Resedaceae, based on morphological features, chromosome meiotic behaviour, karyotype features, size and fertility of pollen grains, nucleotypic parameters, seed protein profiles and esterase isozyme patterns.For the comparison of the seed protein profiles among species a method was developed based on the presence or absence of the bands by means of a computer program. The dendrogram obtained by such a method is in line, to a great extent, with the clusters (sections) obtained within the family based on morphological features.Data on meiotic behaviour and on morphology, such as the type of fruit, carpel numbers and others, suggest that x=5 is the primitive basic chromosome number of this family. x₁=6 and x₂=7 are considered as secondary basic numbers derived from x=5 through aneuploid changes.The results support a proposed phylogenetic tree of the genera and sections of the genus Reseda represented in the European Flora.The principal phenomena that have operated in the evolution of the Resedaceae seem to be aneuploid changes, polyploidy and structural rearrangements. A trend towards DNA increase in the evolution of this group is also apparent.     

Moniliformin production byFusarium species isolated from Argentinian corn

Forty-one isolates ofFusarium obtained from the main Argentinian corn production area were tested for their ability to produce moniliformin. One of 22 isolates ofF. moniliforme, 2/10 of F.proliferatum and 3/9 ofF. subglutinans, produced moniliformin in a range between 0,3 to 2,7 mg/g. These data represent the first report of the production of moniliformin byFusarium species from section Liseola in Argentina.     

Simultaneous high-biomass protein production and nutrient removal using Spirulina maxima in sea water supplemented with anaerobic effluents

Maximum protein accumulation (71%, w/w) and nutrient removal by a mutant strain of Spirulina maxima growing on sea water supplemented with anaerobically treated pig slurry was achieved at 30°C with constant illumination (60 to 70 Em^-2s^-1), using a flow rate of 14.5 cm s^-1 (20 rev. min^-1 of a paddle wheel). Total phosphates were decreased by 99% and all ammonia-N was removed under these conditions.The authors are with the Department of Environmental Biotechnology, Institute of Ecology, Aptd Postal 63, Xalapa, Ver., Mexico     

Effect of photoperiod and exogenous melatonin on correlates of estrus in the domestic rabbit

It was the purpose of this study to test whether inhibition of estrus in the rabbit by short photoperiod could be simulated by subcutaneous implants of the pineal hormone melatonin. By measuring two non-invasive and readily quantifiable correlates of estrus, emission of the so-called nipple-search pheromone and scent-marking behavior (chinning), it was found that:

1. In intact does kept in stimulatory long photoperiod, melatonin suppressed chinning but had no effect on emission of nipple-search pheromone.
2. In intact, melatonin-treated does which were returned from inhibitory short day to stimulatory long day, chinning remained suppressed, whereas pheromone emission increased as for the vehicle-treated, control does.
3. In ovariectomized does, estradiol administration stimulated both pheromone emission and chinning whereas melatonin failed to suppress these effects.

Thus, although the administration of melatonin had an inhibitory effect on chinning it failed to suppress emission of the nipple-search pheromone and therefore failed to fully simulate the effect of short photoperiod on these two correlates of estrus. Several explanations for this discrepancy are considered, including the possibility that melatonin is not the sole mediary of the photoperiodic response, and that at least in female rabbits, other pineal products may also play a significant role.