Effects of magnesium availability on the activity of plasma membrane ion transporters and light-induced responses from broad bean leaf mesophyll

Considering the physiological significance of Mg homeostasis in plants, surprisingly little is known about the molecular and ionic mechanisms mediating Mg transport across the plasma membrane and the impact of Mg availability on transport processes at the plasmalemma. In this study, a non-invasive ion-selective microelectrode technique (MIFE) was used to characterize the effects of Mg availability on the activity of plasma membrane H⁺, K⁺, Ca²⁺, and Mg²⁺ transporters in the mesophyll cells of broad bean (Vicia faba L.) plants. Based on the stoichiometry of ion-flux changes and results of pharmacological experiments, we suggest that at least two mechanisms are involved in Mg²⁺ uptake across the plasma membrane of bean mesophyll cells. One of them is a non-selective cation channel, also permeable to K⁺ and Ca²⁺. The other mechanism, operating at concentrations below 30 M, was speculated to be an H⁺/Mg⁺ exchanger. Experiments performed on leaves grown at different levels of Mg availability (from deficient to excessive) showed that Mg availability has a significant impact on the activity of plasma-membrane transporters for Ca²⁺, K⁺, and H⁺. We discuss the physiological significance of Mg-induced changes in leaf electrophysiological responses to light and the ionic mechanisms underlying this process.     

Is lack of morning sickness teratogenic? A prospective controlled study

BACKGROUND: Case-control studies have suggested that the nausea and vomiting of pregnancy (NVP) may have a protective effect against specific malformations. These suggestions have been interpreted as if the lack of NVP may put mothers at an increased teratogenic risk. METHODS: A prospective, cohort-controlled study was done comparing pregnancy outcome in women not experiencing NVP with those experiencing NVP at two levels of clinical severity. Women who called the Motherisk program about first-trimester exposure to drugs and who had not experienced NVP were included as the study group. The NVP Healthline enrolled two control groups of women with NVP treated with a doxylamine-pyridoxine combination for morning sickness. These women were exposed during the first trimester of gestation to either higher than the standard dose (5-12 tablets/day) or a standard dose (1-4 tablets/day) of doxylamine-pyridoxine. The women in all three groups were followed up four to six months after the expected date of birth to ascertain pregnancy outcomes and child health. RESULTS: There were no major malformations among offspring of 130 women not experiencing NVP. There were two major malformations among 246 women experiencing NVP. The two control groups of women with NVP had similar distributions of gestational ages, birth rates, as well as rates of miscarriages and stillbirths, as in the no-NVP group. CONCLUSIONS: This study did not show an association between lack of NVP and an increase in the overall rates of major malformations.     

Comprehensive analysis of metabolites in Corynebacterium glutamicum by gas chromatography/mass spectrometry

An analytical method based on gas chromatography/mass spectrometry was developed for metabolome investigation of Corynebacterium glutamicum. For the first time a fast method for metabolic screening that can be automated is described for this organism. More than 1000 compounds could be detected per experiment, ca. 330 of those showed a peak area significantly above background. Out of these 164 compounds were identified so far, representing derivatives of 121 different metabolites, which were quantified in one sample. In spite of the different chemical nature of metabolites and high matrix content, a measurement reproducibility in the range of 6% error was achieved. The application of this method for the analysis of the adaptation of C. glutamicum to different growth conditions is demonstrated.     

Synthetic model and bioactive peptides as potential substrates for enteropeptidase

Enteropeptidase (enterokinase EC 3.4.21.9), catalyzing trypsinogen activation, exhibits unique properties for high efficiency hydrolysis of the polypeptide chain after the N-terminal tetraaspartyl-lysyl sequence. This makes it a convenient tool for the processing of fusion proteins containing this sequence. We found the enteropeptidase-catalysing degradation of some bioactive peptides: cattle hemoglobin beta-chain fragments Hb (2–8) (LTAEEKA) and Hb (1–9) (MLTAEEKAA), human angiotensin II (DRVYIHPF) (AT). Model peptideswith truncated linker WDDRG and WDDKG also were shown to be susceptible to enteropeptidase action. Kinetic parameters ofenteropeptidase hydrolysis for these substrates were determined.K _m values for all substrates with truncated linker (10^-3 M) are an order of magnitude higher thancorresponding values for typical enteropeptidase artificial peptide or fusion protein substrates with full enteropeptidase linker –DDDDK– (K _m 10^-4 M). k _cat values for AT, Hb (2–8), WDDRG and WDDKG are 30–40 min^-1. But one additional amino acid residue at both N- and C-terminus of Hb (2–8) results in a drastic increase of hydrolysis efficiency: k _cat value for Hb (1–9) is 1510 min^-1. Recent study demonstrates the possibility of undesirable cleavage of target peptides or proteins containing the above-mentioned truncated linker sequences; further, the ability of enteropeptidase to hydrolyse specifically several biologically active peptides in vitro along with its unique natural substrate trypsinogen was demonstrated.     

Effects of maternal occupational exposure to organic solvents on offspring visual functioning: a prospective controlled study

BACKGROUND: Previous studies in adults and animals with high level exposure to organic solvents suggested impairments in visual functioning. The objective of this pilot study was to examine the effects of maternal occupational exposure to organic solvents during pregnancy on offspring color vision and visual acuity, the development of which may be especially vulnerable to organic solvent exposure. METHODS: We conducted a prospective cohort study of 32 offspring of women who were exposed occupationally to organic solvents during pregnancy compared with 27 nonexposed children. Monocular and binocular color vision and visual acuity were assessed using the Minimalist Test and the Cardiff Cards, respectively. Children with known hereditary color vision loss were excluded. RESULTS: Solvent-exposed children had significantly higher error scores on red-green and blue-yellow color discrimination, as well as poorer visual acuity compared with the control group. Exposure index (an estimated measure of exposure intensity) was not significantly related to color discrimination or visual acuity score. Despite excluding all children with a known family history of color vision loss, clinical red-green color vision loss was found among 3 of the 32 exposed children compared with none of the matched controls. CONCLUSIONS: These preliminary findings suggest that occupational exposure to organic solvents during pregnancy is associated with an increased risk of color vision and visual acuity impairment in offspring. The importance of routine visual function screening in risk assessment after prenatal exposure to chemicals warrants further attention.     

Identification and Analysis of the Polyhydroxyalkanoate-Specific β-Ketothiolase and Acetoacetyl Coenzyme A Reductase Genes in the Cyanobacterium Synechocystis sp. Strain PCC6803

Synechocystis sp. strain PCC6803 possesses a polyhydroxyalkanoate (PHA)-specific β-ketothiolase encoded by phaA_Syn and an acetoacetyl-coenzyme A (CoA) reductase encoded by phaB_Syn. A similarity search of the entire Synechocystis genome sequence identified a cluster of two putative open reading frames (ORFs) for these genes, slr1993 and slr1994. Sequence analysis showed that the ORFs encode proteins having 409 and 240 amino acids, respectively. The two ORFs are colinear and most probably coexpressed, as revealed by sequence analysis of the promoter regions. Heterologous transformation of Escherichia coli with the two genes and the PHA synthase of Synechocystis resulted in accumulation of PHAs that accounted for up to 12.3% of the cell dry weight under high-glucose growth conditions. Targeted disruption of the above gene cluster in Synechocystis eliminated the accumulation of PHAs. ORFs slr1993 and slr1994 thus encode the PHA-specific β-ketothiolase and acetoacetyl-CoA reductase of Synechocystis and, together with the recently characterized PHA synthase genes in this organism (S. Hein, H. Tran, and A. Steinbüchel, Arch. Microbiol. 170:162–170, 1998), form the first complete PHA biosynthesis pathway known in cyanobacteria. Sequence alignment of all known short-chain-length PHA-specific acetoacetyl-CoA reductases also suggests an extended signature sequence, VTGXXXGIG, for this group of proteins. Phylogenetic analysis further places the origin of phaA_Syn and phaB_Syn in the γ subdivision of the division Proteobacteria.