Crystal structure of nitrogen regulatory protein IIA<Superscript>Ntr</Superscript> from <Emphasis Type="Italic">Neisseria meningitidis</Emphasis>

Background  

The NMB0736 gene of Neisseria meningitidis serogroup B strain MC58 encodes the putative nitrogen regulatory protein, IIA^Ntr (abbreviated to NM-IIA^Ntr). The homologous protein present in Escherichia coli is implicated in the control of nitrogen assimilation. As part of a structural proteomics approach to the study of pathogenic Neisseria spp., we have selected this protein for structure determination by X-ray crystallography.     

Maternal to fetal transfer of free fatty acids in the in situ perfused rabbit placenta

The transfer of free fatty acids (FFA) across the placenta perfused in situ was studied in anaesthetised rabbits in late gestation. [14C]Palmitic acid and antipyrine were infused into 11 pregnant rabbits and samples collected for up to 90 min from the mother and the umbilical vessels. Levels of total FFA, radioactivity and antipyrine, a marker of placental integrity, were measured. Net FFA flux across the placenta increased with maternal FFA concentrations, confirming observations made using different methods. The specific activity of [14C]palmitic acid in perfusate also related to maternal levels and indicated that almost half of the FFA crossing the rabbit placenta must be derived from sources other than circulating maternal FFA. The composition of the perfusate FFA had a profile similar to that of circulating maternal FFA, except for an increase in a number of long chain, polyunsaturated fatty acids. These findings are consistent with maternal triacylglycerol as the other fatty acid source, with the placenta adding the longer chain, polyunsaturated fatty acids.     

Crystal structure of cat muscle pyruvate kinase at a resolution of 2.6 A

The structure of pyruvate kinase (EC 2.7.1.40) has been determined from a 2.6 Å resolution electron density map. This map shows more detail than the previous 3.1 Å map (Stammers &; Muirhead, 1977) and has enabled a detailed chain folding to be established for two out of the three domains which make up each of the four identical subunits. A provisional chain folding has been established for the third domain. The results have been briefly reported in a previous paper (Levine et al., 1978). Details of the structure determination and a further discussion of the results are presented in this paper.Domain A (the three domains of pyruvate kinase are referred to as A, B and C) can be described in terms of a cylindrical eight-stranded parallel β sheet and an outer coaxial cylinder of eight α helices. The α helices connect adjacent strands of the β sheet. Domain B is made up of a closed anti-parallel β sheet structure. Domain C is a five-stranded β sheet of which the fourth strand is anti-parallel and the rest parallel. These strands are also interconnected by α helices.Domain A can be dissected into eight consecutive β strand—α helix units starting from the N-terminus. The arrangement of these relative to each other can be most simply described by relating them to eight planes, each at 40 ° to the cylinder axis and symmetrically placed around the cylinder. When unit 2 is aligned with one of these planes then units 1, 3, 4, 5 and 8 are also closely aligned with a plane. This analysis is also applied to triosephosphate isomerase and a strikingly similar arrangement is found. A detailed comparison of the two structures is presented. Although the lack of a chemical sequence makes it difficult to identify the amino acid residues of pyruvate kinase, side-chains are clearly visible in the map and this information is correlated with the results of previous 6 Å substrate soaking experiments and with the structure of triosephosphate isomerase. The similarities and differences are discussed in terms of similarities and differences in the reactions catalysed and also of different subunit packing.     

Studies on the endogenous phospholipids of chick embryo myocardium and their in vitro hydrolysis by endogenous phospholipases during embryogenesis

The phospholipid profiles of the myocardium (from 10- and 18-day old chick embryos and 13-day old chick) and their in vitro response to the endogenous lipolytic enzymes (mainly of the phospholipase group) at pH 7.4 and 38 degrees C for 60 min were analyzed by TLC technology and densitometry. Cardiolipin (CL) was shown to be one of the major phospholipids of the chick embryo myocardium and its concentration increased as the chick embryo advanced in development. Monolysocardiolipin (MLCL) was produced subsequent to in vitro incubation of whole tissue homogenates in all myocardia studied as well as a concurrent reduction in CL. This deacylation of CL increased in magnitude as the chick embryo advanced in development indicating its age relatedness. The level of phosphatidyl ethanolamine (PE) plasmalogen was also high in all myocardia studied. Lyso alkenyl PE (LPE) was produced subsequent to in vitro incubation and its level increased as the chick embryo advanced in development, indicating PLA(2) action on the sn-2 fatty acid of PE. Phosphatidyl choline (PC) plasmalogen was also present in the chick embryo myocardium and its level increased gradually as the chick embryo advanced in development. In contrast, yolk-sac membrane contains very minute amounts of CL and PE. No PC was detected and no LPE was formed following in vitro incubation. The yolk of the unfertilized chicken egg has no CL and has very minute amounts of PE, no PC and no lysophospholipids were detected following in vitro incubation in all samples analyzed.     

Floral reward production is timed by an insect pollinator

Interval timing--sensitivity to elapsing durations--has recently been found to occur in an invertebrate pollinator, the bumble-bee (Bombus impatiens). Here, bumble-bees were required to time the interval between the start of foraging in a patch of low-quality artificial flowers providing 25% sucrose and the availability of a high-quality flower (HQF) that provided 50% sucrose after a fixed delay. The delay changed after every 20 foraging bouts in the order 30-150-30 s. Bees visited the HQF sooner when the delay was 30 s than when it was 150 s, and visits to the HQF peaked near the end of both delays. When the delay changed to 150 s, bees appeared to time both the previous 30 s delay and the new delay. To examine whether bees also learned what kind of reward was provided at the HQF, its usual reward was replaced with 25% sucrose in a final foraging bout. Bumble-bees rejected the HQF on the reward-replacement test. These results show that bumble-bees remembered both when reward was produced by the HQF and what type of reward was produced. These findings indicate that bumble-bees can learn both the timing and content of reward production.     

Amendments and their combined application for enhanced copper, cadmium, lead uptake by Lolium perenne

Chemical amendments can enhance heavy metal phytoextraction by increasing metal bioavailability for plant root uptake and translocation to shoots, and by improving plant growth. This study assessed the effect of various amendments on plant growth and metal uptake over a 30-day period. An aminopolycarboxylic acid (EDDS), amino acid (histidine), organic acid (citric acid), biosurfactant (rhamnolipid), and inorganic ligand (sulfate) were applied as amendments individually or in combination to hydroponically grown ryegrass (Lolium perenne cv. SR4500) in the presence of a metal (Cu, Cd or Pb). EDDS (1 mM) was the most effective amendment (individually and in combinations) for enhancing Cu and Pb uptake to shoot tissue, while histidine was beneficial for increasing both Cu and Cd uptake. Individual treatments of citric acid, rhamnolipid and sulfate moderately enhanced shoot concentrations of Cu and Cd only. The combination of EDDS, rhamnolipid and citric acid resulted in the highest shoot metal levels, but also caused severe phytotoxicity. Translocation to shoot tissue was generally greater for amendments with higher affinity for the metal of interest, and metal mobility appeared to be influenced by speciation. Due to potential toxicity, amendment combinations may be more effective when applied shortly before harvesting.