Oxygen inhibition of nitrate uptake is a general regulatory mechanism in nitrate respiration

It has recently been demonstrated that oxygen inhibits nitrate uptake by denitrifying Pseudomonas aeruginosa. The purpose of the present investigation was to determine if this novel mechanism of regulation is universal for the regulation of nitrate respiration in other widely divergent species of bacteria. Nitrate transport by whole cell suspensions was completely and reversibly inhibited in 11 out of 12 species tested, whereas nitrate reduction by cell-free extracts was not affected by oxygen or was only partially inhibited in some cases. These results indicate that oxygen inhibition of nitrate uptake is a general regulatory phenomenon.     

Topology of Xer recombination on catenanes produced by lambda integrase.

Xer site-specific recombination at the psi site from plasmid pSC101 displays topological selectivity, such that recombination normally occurs only between directly repeated sites on the same circular DNA molecule. This intramolecular selectivity is important for the biological role of psi, and is imposed by accessory proteins PepA and ArcA acting at accessory DNA sequences adjacent to the core recombination site. Here we show that the selectivity for intramolecular recombination at psi can be bypassed in multiply interlinked catenanes. Xer site-specific recombination occurred relatively efficiently between antiparallel psi sites located on separate rings of right-handed torus catenanes containing six or more nodes. This recombination introduced one additional node into the catenanes. Antiparallel sites on four-noded right-handed catenanes, the normal product of Xer recombination at psi, were not recombined efficiently. Furthermore, parallel psi sites on right-handed torus catenanes were not substrates for Xer recombination. These findings support a model in which psi sites are plectonemically interwrapped, trapping a precise number of supercoils that are converted to four catenation nodes by Xer strand exchange.     

Small bowel and colon glucose absorption study in rats by an adaptation of Sols and Ponz method.

An adaptation of the Sols and Ponz method for the study of glucose intestinal absorption was developed by considering the special conditions of our line research. The glucose absorption was studied in proximal jejunum, distal ileum and distal colon in Wistar rat. The main adaptations in the method for successive absorptions with intestinal perfusions in vivo were the length of the intestinal segment and the change of the pumping system. The results are very similar to those obtained with the original method.     

Effect of nitroammofoska on the aldolase activity of the normal hemolymph in the mollusk Planorbarius banaticus and in trematode invasion

The infection of Planorbarius banaticus with sporocysts of Cotylurus cornutus is accompanied by an increase in aldolase activity of molluscs' haemolymph of 1.2 fold. In solutions of nitroammofoska (0.1, 1 and 10 mg/1) the activity of this ferment in infected individuals increases much higher than in non-infected ones. This results in fast carbohydrate expenditures by molluscs, intermediate hosts of trematodes, and their death from exhaustion.     

Cytogenetic analysis of mouse metaphase II oocytes following exposure to tritiated water

Female mice were given different dosages (0, 3.0, 7.5, 15.0, or 30 muCi/ml) of tritium in their drinking water continuously from 3 to 7 weeks of age to assess the effects on germ cell chromosomes. At 8-9 weeks of age, mice were superovulated and metaphase II oocytes were processed and C-banded for cytogenetic analyses. Chromatid acentric fragments were the only type of structural aberration detected, and their incidence was higher in controls than in any of the tritiated water (HTO) groups. Analysis of numerical chromosomal aberrations revealed that the incidence of hypoploid (N = 19) oocytes was higher in oocytes from mice who drank HTO as compared with controls. However, the effects of HTO upon aneuploidy induction was not definitive due to the increase the incidence of aberrations in mouse oocytes can be related to the low dose rate resulting from chronic HTO exposure and possibly death of tritium-damaged cells.