Intraspecific variability in the alkaloid metabolism of Galanthus elwesii

Alkaloid pattern of individuals from 16 Bulgarian Galanthus elwesii populations was investigated by GC/MS and TLC. Twenty-one Amaryllidaceae alkaloids were detected and 14 of them were identified. Crinane type alkaloids, haemanthamine or crinine, dominated alkaloid metabolism in most of the populations. With exception of one population, where the separate individuals showed variable alkaloid profiles (dominated by crinine or haemanthamine) the individuals of the rest of populations have identical and characteristic alkaloid profiles. Some populations showed remarkable differences in respect to their alkaloid pattern-type of biosynthesis, main alkaloids and number of alkaloids. Populations dominated by galanthamine type alkaloids were found as well. These data demonstrate that like the morphological features, the alkaloid metabolism of G. elwesii is also variable.     

Comprehensive analysis of polyamine transport and biosynthesis in the dominant human gut bacteria: Potential presence of novel polyamine metabolism and transport genes

Recent studies have reported that polyamines in the colonic lumen might affect animal health and these polyamines are thought to be produced by gut bacteria. In the present study, we measured the concentrations of three polyamines (putrescine, spermidine, and spermine) in cells and culture supernatants of 32 dominant human gut bacterial species in their growing and stationary phases. Combining polyamine concentration analysis in culture supernatant and cells with available genomic information showed that novel polyamine biosynthetic proteins and transporters were present in dominant human gut bacteria. Based on these findings, we suggested strategies for optimizing polyamine concentrations in the human colonic lumen via regulation of genes responsible for polyamine biosynthesis and transport in the dominant human gut bacteria.     

Chromosomal localization of genes involved in biosynthesis,metabolism or transport of cholesterol in the rat

Several genes involved in biosynthesis, transport or metabolism of cholesterol have been localized on rat chromosomes by using a radiation hybrid (RH) panel. The genes, coding for squalene epoxidase (Sqle), mevalonate kinase (Mvk), and farnesyl diphosphate farnesyl transferase 1 (Fdft1) which are involved in cholesterol biosynthesis, have been mapped on chromosome 7, 12, and 15, respectively. The genes coding for phospholipid transfer protein (Pltp), sterol carrier protein-2 (Scp2), ATP binding cassette reporter A7 (Abca7), scavenger receptor class B, type 1 (Cd36l1), steroidogenic acute regulatory protein (Star), and lecithin:cholesterol acyl transferase (Lcat), which are involved in the transfer and/or metabolism of cholesterol, have been mapped on chromosome 3, 5, 7, 12, 16, and 19, respectively. Each of the genes Scp2, Sqle and Fdft1 maps close to a QTL for serum total cholesterol in rat, suggesting that these three genes might represent candidate genes for the previously mapped QTLs.     

Role of nitrogen and carbon transport, regulation, and metabolism genes for Saccharomyces cerevisiae survival in vivo

Saccharomyces cerevisiae is both an emerging opportunistic pathogen and a close relative of pathogenic Candida species. To better understand the ecology of fungal infection, we investigated the importance of pathways involved in uptake, metabolism, and biosynthesis of nitrogen and carbon compounds for survival of a clinical S. cerevisiae strain in a murine host. Potential nitrogen sources in vivo include ammonium, urea, and amino acids, while potential carbon sources include glucose, lactate, pyruvate, and fatty acids. Using mutants unable to either transport or utilize these compounds, we demonstrated that no individual nitrogen source was essential, while glucose was the most significant primary carbon source for yeast survival in vivo. Hydrolysis of the storage carbohydrate glycogen made a slight contribution for in vivo survival compared with a substantial requirement for trehalose hydrolysis. The ability to sense and respond to low glucose concentrations was also important for survival. In contrast, there was little or no requirement in vivo in this assay for any of the nitrogen-sensing pathways, nitrogen catabolite repression, the ammonium- or amino acid-sensing pathways, or general control. By using auxotrophic mutants, we found that some nitrogenous compounds (polyamines, methionine, and lysine) can be acquired from the host, while others (threonine, aromatic amino acids, isoleucine, and valine) must be synthesized by the pathogen. Our studies provide insights into the yeast-host environment interaction and identify potential antifungal drug targets.     

Proline metabolism and transport in plant development

Proline fulfils diverse functions in plants. As amino acid it is a structural component of proteins, but it also plays a role as compatible solute under environmental stress conditions. Proline metabolism involves several subcellular compartments and contributes to the redox balance of the cell. Proline synthesis has been associated with tissues undergoing rapid cell divisions, such as shoot apical meristems, and appears to be involved in floral transition and embryo development. High levels of proline can be found in pollen and seeds, where it serves as compatible solute, protecting cellular structures during dehydration. The proline concentrations of cells, tissues and plant organs are regulated by the interplay of biosynthesis, degradation and intra- as well as intercellular transport processes. Among the proline transport proteins characterized so far, both general amino acid permeases and selective compatible solute transporters were identified, reflecting the versatile role of proline under stress and non-stress situations. The review summarizes our current knowledge on proline metabolism and transport in view of plant development, discussing regulatory aspects such as the influence of metabolites and hormones. Additional information from animals, fungi and bacteria is included, showing similarities and differences to proline metabolism and transport in plants.     

Deoxycytidine transport and metabolism in choroid plexus

In vitro, the transport into and release of [3H]deoxycytidine from the isolated choroid plexus, the anatomical locus of the blood-cerebrospinal fluid barrier, were studied separately. By use of the ability of nitrobenzylthioinosine (NBTI) to inhibit deoxycytidine efflux from choroid plexus, the transport of 1 microM [3H]deoxycytidine into choroid plexus at 37 degrees C was measured. Deoxycytidine was transported into choroid plexus against a concentration gradient by a saturable process that depended on intracellular energy production, but not intracellular binding or metabolism. The Michaelis-Menten constant (KT) for the active transport of deoxycytidine into choroid plexus was 15 microM. The active transport system for deoxycytidine was inhibited by naturally occurring nucleosides and deoxynucleosides, but not by 1 mM probenecid and 2-deoxyribose or 100 microM cytosine and cytosine arabinoside. With less than 1 microM [3H]deoxycytidine in the medium, the choroid plexus accumulated [3H]deoxycytidine against a concentration gradient. However, approximately 50% of the [3H]deoxycytidine was phosphorylated to [3H]deoxycytidine nucleotides at a low extracellular [3H]deoxycytidine concentration (6 nM) in 15-min incubations. This accumulation process depended, in part, on saturable intracellular phosphorylation. These studies provide further evidence that the choroid plexus contains an active nucleoside transport system of low specificity for deoxynucleosides and ribonucleosides, and a separate, saturable efflux system for deoxynucleosides which is very sensitive to inhibition by NBTI.     

Citrate transport and metabolism in mammalian cells

Citrate, an organic trivalent anion, is a major substrate for generation of energy in most cells. It is produced in mitochondria and used either in the Krebs' cycle or released into cytoplasm through a specific mitochondrial carriers. Citrate can also be taken up from blood through different plasma membrane transporters. In the cytoplasm, citrate can be used ultimately for fatty acid synthesis, which is increased in cancer cells. Here, we review the ways in which citrate can be transported and discuss the changes in transport and metabolism that occur in cancer cells. The primary focus is on the prostate gland, which is known to produce and release large amounts of citrate during its normal secretory function. The significant changes that occur in citrate‐related metabolism and transport in prostate cancer are the second focus. This review strives to relate these mechanisms to molecular biology on the one hand and to clinical applications on the other.     

P metabolism and transport in AM fungi

The arbuscular mycorrhizal symbiosis is mutualistic, based on reciprocal transfer of P from the fungus to the plant and carbon from the plant to the fungus. Thus P is a most important `currency' in the symbiosis. After absorbing P from the soil solution, the fungi first incorporate it into the cytosolic pool, and the excess P is transferred to the vacuoles. The vacuolar P pool probably plays a central role in P supply to the plant. The main forms of inorganic P in fungal vacuoles are orthophosphate and polyphosphate, but organic P molecules may also be present. Long distance translocation of P from the site of uptake in the external mycelium to the site of transfer to the plant is probably achieved via transfer of vacuolar components. This transport would be mediated either by protoplasmic streaming or the motile tubular vacuole-like system. The site of release of P into the interfacial apoplast and thence to the plant is most probably the fungal arbuscules. The biochemical and biophysical processes involved in P metabolism and transfer between cellular compartments in the symbiosis are currently not well understood. Some recent investigations of substrate specificities of phosphatase-type enzymes in AM fungi and other eukaryotic microorganisms, however, have shed new light on earlier results and permit the construction of a hypothetical scheme of P-flow, including possible regulatory factors. Steps in this scheme are experimentally testable and should stimulate future research.     

Proline transport and metabolism in Rickettsia prowazekii

Purified Rickettsia prowazekii cells were able to transport L-proline. The influx of this amino acid had a Kt of 14 microM and a Vmax of about 64 pmol/min per mg of protein. Proline could not be transported by heat-killed or metabolically poisoned rickettsiae or at 0 degrees C. The uptake of proline was linear for almost 2 h. More than 90% of the accumulated intracellular radioactivity was proline. This intracellular pool could not be chased out of the cell by excess non-radioactive proline and did not exit into a proline-free medium. These results indicate that intracellular proline was bound or that the cell had a very limited efflux component for proline transport. The influx of proline was specific: among various analogs tested, only 3,4-dehydro-D,L-proline was effective in inhibiting proline uptake. R. prowazekii cells were unable to utilize proline as an energy source to drive hemolysis, and no measurable evolution from the rickettsiae of CO2 derived from proline occurred. The activities of the enzymes pyrroline-5-carboxylate-reductase and pyrroline-5-carboxylate dehydrogenase were not detectable. These enzymes are important in anabolism and catabolism of proline, respectively, and, if present in R. prowazekii have activities less than 1% of those in Escherichia coli.     

D-mannose transport and metabolism in isolated enterocytes

D-mannose transport and metabolism has been studied in enterocytes isolated from chicken small intestine. In the presence of Na(+), the mannose taken up by the cells either remains free, is phosphorylated, is catabolized to H(2)O, or becomes part of membrane components. The mannose remaining free in the cytosol is released when the cells are transferred to an ice bath. The Na(+)-dependent D-mannose transport is electrogenic and inhibited by ouabain and dinitrophenol; its substrate specificity differs from SGLT-1 transporter. The Glut2 transporter inhibitors phloretin and cytochalasin B added following 30-min mannose uptake reduced the previously accumulated D-mannose, whereas these two agents increased the cell to external medium 3-O-methyl-glucose (3-OMG) concentration ratio. D-mannose efflux rate from preloaded D-[2-(3)H]-mannose enterocytes is Na(+)-independent. Phloretin did not affect D-mannose efflux rate, whereas it inhibited that of 3-OMG. Neither mannose uptake nor efflux rate were affected by fructose. It is concluded that part of the mannose taken up by the enterocytes is rapidly metabolized and that enterocytes have two D- mannose transport systems: one is concentrative and Na(+)-dependent and the other is Na(+)-independent and passive.     

Cloning of the Escherichia coli sor genes for L-sorbose transport and metabolism and physical mapping of the genes near metH and iclR.

The sor genes for L-sorbose (Sor) degradation of Escherichia coli EC3132, a wild-type strain, have been cloned on a 10.8-kbp fragment together with parts of the metH gene. The genes were mapped by restriction analysis, by deletion mapping, and by insertion mutagenesis with Tn1725. Seven sor genes with their corresponding gene products have been identified. They form an operon (gene order sorCpCDFBAME) inducible by L-sorbose, and their products have the following functions: SorC (36 kDa), regulatory protein with repressor-activator functions; SorD (29 kDa), D-glucitol-6-phosphate dehydrogenase; SorF and SorB (14 and 19 kDa, respectively), and SorA and SorM (27 and 29 kDa, respectively), two soluble and two membrane-bound proteins, respectively, of an L-sorbose phosphotransferase transport system; SorE (45 kDa), sorbose-1-phosphate reductase. The sor operon from E. coli EC3132 thus is identical to the operon from Klebsiella pneumoniae KAY2026. On the basis of restriction mapping followed by Southern hybridization experiments, the sor genes were mapped at 91.2 min on the chromosome, 3.3 kbp downstream of the metH-iclR gene cluster, and shown to be transcribed in a counterclockwise direction. The chromosomal map of the Sor+ strain EC3132 differs from that of the Sor- strain K-12 in approximately 8.6 kbp.