Efficient use and recycling of the micronutrient iodide in mammals

Daily ingestion of iodide alone is not adequate to sustain production of the thyroid hormones, tri- and tetraiodothyronine. Proper maintenance of iodide in vivo also requires its active transport into the thyroid and its salvage from mono- and diiodotyrosine that are formed in excess during hormone biosynthesis. The enzyme iodotyrosine deiodinase responsible for this salvage is unusual in its ability to catalyze a reductive dehalogenation reaction dependent on a flavin cofactor, FMN. Initial characterization of this enzyme was limited by its membrane association, difficult purification and poor stability. The deiodinase became amenable to detailed analysis only after identification and heterologous expression of its gene. Site-directed mutagenesis recently demonstrated that cysteine residues are not necessary for enzymatic activity in contrast to precedence set by other reductive dehalogenases. Truncation of the N-terminal membrane anchor of the deiodinase has provided a soluble and stable source of enzyme sufficient for crystallographic studies. The structure of an enzyme·substrate co-crystal has become invaluable for understanding the origins of substrate selectivity and the mutations causing thyroid disease in humans.     

Chromosomal assignment of amplified genes in hydroxyurea-resistant hamster cells

We have shown previously that cDNAs for the M1 and M2 subunits of ribonucleotide reductase, ornithine decarboxylase (ODC), and p5-8, a 55,000-Dalton protein, hybridize to amplified genomic sequences in a highly hydroxyurea-resistant hamster cell line. We have extended these observations to include two additional, independently isolated, hydroxyurea-resistant cell lines: SC8, a single-step hamster ovary cell line, and KH450, a multistep human myeloid leukemic cell line, have also undergone genomic amplification for sequences homologous to ODC and p5-8 cDNAs. However, neither SC8 nor KH450 contains amplified genomic sequences homologous to an M1 cDNA probe. A panel of mouse-hamster somatic cell hybrids was used to map sequences homologous to M1, M2, ODC, and 5-8 cDNAs in the hamster genome. The M2, ODC, and p5-8 cDNAs hybridized to DNA fragments that segregated with hamster chromosome 7. In contrast, M1 cDNA hybridized to DNA fragments that segregated with hamster chromosome 3. These data suggest that the genes RRM2, (M2), ODC, and p5-8, but not RRMI (M1), are linked and may have been co-amplified in the selection of the hydroxyurea-resistant hamster and human cell lines.     

The role of arctic zooplankton in biogeochemical cycles: respiration and excretion of ammonia and phosphate during summer

The study of the structural and functional properties of key components of polar marine ecosystems has received increased attention in order to better understand the ecological consequences of future sea temperature rise and seasonal ice retraction. Owing to this purpose, during the ATOS-Arctic cruise, held in July 2007 in the framework of the 2007–2008 International Polar Year, we studied the respiratory carbon demand of mesozooplankton as well as their contribution to the regeneration of inorganic nitrogen and phosphorus (NH₄-N and PO₄-P) via excretion. The studied area comprised several stations along a latitudinal gradient in the East Greenland current, plus a network of stations NW of the Svalbard islands. The specific respiratory carbon losses and phosphorus (PO₄-P) excretion rates were similar or slightly higher than some reports for Arctic mesozooplankton, but the nitrogen (NH₄-N) excretion rates were higher by a factor of 3 when compared with previous data sets. The mesozooplankton respiratory losses were equivalent to 23% of primary production, and at turn zooplankton contributed by excretion to more than 50% of the N and P required by phytoplankton. Although C:N, C:P and N:P metabolic atomic quotients almost coincided with the average Redfield’s stoichiometric ratios, the low C:N values when compared to previous reports suggested a predominance of protein-related metabolic substrates. The potential consequences of changes observed in the C:N, N:P and C:P metabolic ratios of mesozooplankton for Arctic marine ecosystems are discussed.     

Basal and HCG-stimulated testosterone production by interstitial cells of the Mongolian gerbil (Meriones unguiculatus)--I. Influence of preincubation length, medium composition and temperature

In the absence of HCG, production of testosterone by whole testes superfused in vitro was quite constant during the 5-hr superfusion period. Addition of 23-184 mIU/ml HCG caused a significant increase of testosterone production which was apparent from 30 min after start of superfusion. Basal and HCG-stimulated testosterone production by whole testes was significantly higher (400, 1950 ng/testis/5 hr, without and with 100 mIU HCG) than by isolated cells (200, 1350 ng/testis/5 hr). Incubation of isolated interstitial cells in medium 199 supplemented with fetal calf serum (FCS), (N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid, HEPES) and 3-isobutyl-methylxanthine (MIX), and in medium 199 without FCS, HEPES or MIX, gave similar testosterone responses. While centrifugation at 8000 g for 2 min drastically diminished testosterone formation by isolated interstitial cells, production was similar by cells incubated in either 0.5, 1.0 or 1.5 ml medium. A significant decrease of testosterone synthesis by isolated interstitial cells was found when cells were stored at 4 degrees C for 2 days and then were incubated at 35 degrees C for 6 hr without or with 1-1000 microIU HCG. While isolated interstitial cells incubated at 5 degrees C did not produce testosterone at all, testosterone production increased to 49.5 +/- 3.9 ng/10(5) cells (30 degrees C) and 24.1 +/- 1.1 ng/10(5) cells (40 degrees C), respectively. HCG-stimulated testosterone production was maximal when interstitial cells were incubated at 34 degrees C.     

Interaction of some polyhexamethylene biguanides and membrane phospholipids in Escherichia coli

The interaction between some polyhexamethylene biguanides and the cell envelope of Escherichia coli has been investigated. An amine-ended dimer, (AED, n = 2), a polydisperse mixture (ICI plc) available as the active ingredient of Vantocil IB, (PHMB, n = 5.5), and a high molecular weight fraction, (HMW, n = greater than or equal to 10) of PHMB were used. The sensitivity of batch cultures depleted of magnesium (M-dep), phosphorus (P-dep) or glycerol (C-dep) towards the biocides was assessed by monitoring the rate and extent of potassium ion leakage. P-dep suspensions were particularly resistant to all these agents and possessed less than half the quantity of phospholipid of other cell types. This was compensated for by a proportionate increase in fatty acid and neutral lipid content of the cells. The reduction in phospholipid content was accounted for by decreases in phosphatidylglycerol (PG) and phosphatidylethanolamine (PE). Diphosphatidylglycerol (DPG) and phosphatidylserine (PS) content of the cultures remained unaffected by the depleting nutrient. Fourier-transform n.m.r. spectroscopy was used to study proton nuclei during the interaction of HMW, AED and PHMB with various phospholipid-vesicle preparations. The results strongly suggest that the biocides acted preferentially on the acidic phospholipids PG and DPG, rather than towards PE or PS. Resistance of P-dep cultures therefore reflected reductions in PG content. A molecular basis for the interaction of these compounds and membranes is proposed.     

The release of prostaglandins in human aqueous humour following intraocular surgery. Effect of indomethacin

Inflammatory reaction to ocular trauma is known to be related to prostaglandins. To further evaluate this phenomenon in human, PGE₁ and E₂ were measured by R.I.A. after silicic acid chromatography in aqueous humour of 26 patients before and 3 days after surgery for unilateral senile cataract (posterior chamber implant after extracapsular surgery). 13 out of these patients were treated with indomethacin by enteral route and 13 were not treated.PGE₂ levels increased in all non-treated patients from : m < 214 pg/ml before surgery, to 2666 ± 869 pg/ml (range : 257 - 8728) p < 0.001 after surgery. PGE₂ levels did not increase in indomethacin-treated patients. PGE₁ levels did not increase significantly in non-treated as in treated patients.1) Intra-ocular surgery is followed in human by a constant increase of the only PGE₂ in the aqueous humour. 2) Indomethacin inhibits this increase. 3) The post-surgical increase in the permeability of blood-aqueous barrier appears to be related to a release of PGE₂.     

Mutagenicity testing of dichloromethane in short-term mammalian test systems

Several short-term mammalian test systems were used for mutagenicity testing of the organic solvent dichloromethane. The compound was negative in the forward mutation test on the HGPRT locus in Chinese hamster cells and the unscheduled DNA synthesis test in both human and hamster cells. In the test on DNA synthesis inhibition, dichloromethane caused an aspecific inhibition in both human and hamster cells, but in this test the effect did not indicate a DNA-damaging action. A weak positive effect was found in the test on sister-chromatid exchanges in hamster cells.