Major Transport Form Research Articles

UDP-glucose pyrophosphorylase. An old protein with new tricks.

Sugars are central to a plant's raison d'etre as products of photosynthesis. They are the ultimate source of energy and carbon skeletons for all biomolecules, and they provide the material out of which a plant builds its cell walls, fibers, and wood. Thus, regulation of any activity involved in biosynthesis of sugars, especially Suc (the major transport form of carbon in plants), is of utmost interest in understanding the growth and development strategies of a plant. Sugars are also potent regulators of gene expression, via e.g. a hexokinase (HXK) transduction mechanism that senses hexoses, or via Suc-specific or osmoticum transduction pathways, further underlying the importance of sugars in plant homeostasis.

PvUPS1, an allantoin transporter in nodulated roots of French bean.

Nodulated legumes receive their nitrogen via nitrogen-fixing rhizobia, which exist in a symbiotic relationship with the root system. In tropical legumes like French bean (Phaseolus vulgaris) or soybean (Glycine max), most of the fixed nitrogen is used for synthesis of the ureides allantoin and allantoic acid, the major long-distance transport forms of organic nitrogen in these species. The purpose of this investigation was to identify a ureide transporter that would allow us to further characterize the mechanisms regulating ureide partitioning in legume roots. A putative allantoin transporter (PvUPS1) was isolated from nodulated roots of French bean and was functionally characterized in an allantoin transport-deficient yeast mutant showing that PvUPS1 transports allantoin but also binds its precursors xanthine and uric acid. In beans, PvUPS1 was expressed throughout the plant body, with strongest expression in nodulated roots, source leaves, pods, and seed coats. In roots, PvUPS1 expression was dependent on the status of nodulation, with highest expression in nodules and roots of nodulated plants compared with non-nodulated roots supplied with ammonium nitrate or allantoin. In situ RNA hybridization localized PvUPS1 to the nodule endodermis and the endodermis and phloem of the nodule vasculature. These results strengthen our prediction that in bean nodules, PvUPS1 is involved in delivery of allantoin to the vascular bundle and loading into the nodule phloem.

Quantitative and isotopic analysis of amino acids, allantoin, and allantoic acid in soybeans by LC-MS using the atmospheric pressure chemical ionization method

In this report, we determined whether liquid chromatography mass spectrometry (LC-MS) using the atmospheric pressure chemical ionization (APCI) method could be applied for isotopic analysis of the high polar compounds, allantoin, and allantoic acid, which are the major transport forms of N from soybean nodules. The peak areas of the ion chromatogram of authentic allantoin and allantoic acid obtained by selected ion monitoring (SIM) were proportional to the contents of the compounds. The data obtained from the ion intensity using the scan mode and the area of the ion chromatogram using the SIM mode were entirely consistent with the isotope ratio of the compounds. The allantoin and allantoic acid concentrations in the xylem sap of soybeans at various growth stages were measured by the following two methods using LC-MS; an absolute calibration method and an isotopelabeled internal standard method. The values estimated by the isotope-labeled internal standard method were more consistent with those obtained by the colorimetric method. Furthermore, amino acids could be detected under the same analytical conditions. The 15N ratio of asparagine and aspartic acid in the non-nodulating soybean xylem sap which had been supplied with 15N-labeled nitrate could be measured. These results indicate that LCMS (APCI) is a suitable method for isotopic analysis of high polar compounds, including allantoin and allantoic acid in plant xylem sap and tissues.

Are gap junction membrane plaques implicated in intercellular vesicle transfer?

Gap junction channels are concentrated in specialised plaques of plasma membrane where cells are in close apposition. In this communication evidence is provided showing that these specialised regions of membrane also provide a site for vesicular transfer between cells. Vesicle distribution in eye lenses was found to generally reflect the reported distribution of gap junction membrane plaques. In certain areas of the lens gap junction membrane plaques and vesicles could be seen to form combined, complex structures. Ultrastructure of the vesicle and gap junction membrane plaque complexes was consistent with the vesicles moving through membrane plaques from one lens fibre cell to the next. To investigate whether transport of substances was consistent with intercellular vesicle transfer, transport of various markers was investigated. Time course experiments showing the rate of uptake of various markers into the lens did not show dramatic differences for molecules smaller or larger then gap junction pores formed by connexons. While considered as a primary intercellular transport mechanism in the lens, connexon pores were not the sole agent mediating the observed transport. Other reported mechanisms of intercellular transport in the lens can only account for the movement of relatively small molecules. Vesicular transport may therefore be a major form of transport into the outer lens layers for larger molecules. Implicit in these observations is a new hypothesis for intercellular vesicle movement via gap junction membrane plaques. Intercellular vesicle movement could possibly provide a path for large molecules associated with intact vesicles to be transported into the eye lens tissue.

Motorcycle Taxis and Road Safety in Southwestern Nigeria

Motorcycles have become a major form of commercial transportation in Nigeria over the past decade, due in large part to the economic downturn which has placed the purchase and maintenance of new cars and minibuses beyond the grasp of most. The phenomenon began in the towns of Igbo-Ora and Eruwa in southwestern Oyo State, Nigeria around 1989, and has been observed to have important health risks while at the same time providing essential transportation. The study documented 81 road traffic accidents from hospital records in the town of Igbo-Ora in the six months preceding the survey. An observational component of the study documented that only one among 480 motorcyclists observed wore a helmet. Other safety problems included speed, failure to stop at a junction before entering a main road, wearing non-protective light clothing and slippers, carrying in excess of one passenger, and failure to make appropriate turn signals. Older drivers were observed to perform more safety behaviors than younger ones. A total of 267 commercial motorcycle (taxi) drivers (CMDs) were interviewed. Only 31% had some form of license (including learner permits), only 44.2% had seen a copy of the highway code, and 28.1% were reported to have consumed alcohol during short breaks from work. CMDs who had some form of license were older, owned their motorcycle, and had higher safety self-efficacy scores. Those who had seen the highway code, which is published in English, were more educated and had longer years of driving experience, higher safety self-efficacy scores, and greater road safety knowledge. Drinking alcohol during the workday was negatively associated with safety self-efficacy, safety opinion scores, and ownership of the motorcycle. Health education based in the CMD union, school health education, and public advocacy to make consumers/passengers aware of safety issues is recommended.

Protein-protein interactions between sucrose transporters of different affinities colocalized in the same enucleate sieve element.

Suc represents the major transport form for carbohydrates in plants. Suc is loaded actively against a concentration gradient into sieve elements, which constitute the conduit for assimilate export out of leaves. Three members of the Suc transporter family with different properties were identified: SUT1, a high-affinity Suc proton cotransporter; SUT4, a low-affinity transporter; and SUT2, which in yeast is only weakly active and shows features similar to those of the yeast sugar sensors RGT2 and SNF3. Immunolocalization demonstrated that all three SUT proteins are localized in the same enucleate sieve element. Thus, the potential of Suc transporters to form homooligomers was tested by the yeast-based split-ubiquitin system. The results show that both SUT1 and SUT2 have the potential to form homooligomers. Moreover, all three Suc transporters have the potential to interact with each other. As controls, a potassium channel and a monosaccharide transporter, expressed in the plasma membrane, did not interact with the SUTs. The in vivo interaction between the functionally different Suc transporters indicates that the membrane proteins are capable of forming oligomeric structures that, like mammalian Glc transporter complexes, might be of functional significance for the regulation of transport.

Low and high affinity amino acid H+-cotransporters for cellular import of neutral and charged amino acids.

Amides and acidic amino acids represent the major long distance transport forms of organic nitrogen. Six amino acid permeases (AAPs) from Arabidopsis mediating transport of a wide spectrum of amino acids were isolated. AAPs are distantly related to plasma membrane amino acid transport systems N and A and to vesicular transporters such as VGAT from mammals. A detailed comparison of the properties by electrophysiology after heterologous expression in Xenopus oocytes shows that, although capable of recognizing and transporting a wide spectrum of amino acids, individual AAPs differ with respect to specificity. Apparent substrate affinities are influenced by structure and net charge and vary by three orders of magnitude. AAPs mediate cotransport of neutral amino acids with one proton. Uncharged forms of acidic and basic amino acids are cotransported with one proton. Since all AAPs are differentially expressed, different tissues may be supplied with a different spectrum of amino acids. AAP3 and AAP5 are the only transporters mediating efficient transport of the basic amino acids. In vivo competition shows that the capability to transport basic amino acids in planta might be overruled by excess amides and acidic amino acids in the apoplasm. With the exception of AAP6, AAPs do not recognize aspartate; only AAP6 has an affinity for aspartate in the physiologically relevant range. This property is due to an overall higher affinity of AAP6 for neutral and acidic amino acids. Thus AAP6 may serve a different role either in cooperating with the lower affinity systems to acquire amino acids in the low concentration range, as a system responsible for aspartate transport or as an uptake system from the xylem. In agreement, a yeast mutant deficient in acidic amino acid uptake at low aspartate concentrations was complemented only by AAP6. Taken together, the AAPs transport neutral, acidic and cationic amino acids, including the major transport forms, i.e. glutamine, asparagine and glutamate. Increasing proton concentrations strongly activate transport of amino acids. Thus the actual apoplasmic concentration of amino acids and the pH will determine what is transported in vivo, i.e. major amino acids such as glutamine, asparagine, and glutamate will be mobilized preferentially.

Immunolocalization of glutamine synthetase in senescing tobacco (Nicotiana tabacum L.) leaves suggests that ammonia assimilation is progressively shifted to the mesophyll cytosol.

Glutamine synthetase (GS) catalyses the formation of glutamine (a major form of nitrogen transport in plants) in an ATP-dependent reaction using ammonium and glutamate. This enzyme is present in the plastids and/or in the cytosol depending on the plant or the organ examined. In order to understand the role of GS isoforms in the remobilization of leaf nitrogen, we studied the localization of GS isoenzymes during natural senescence of tobacco (Nicotiana tabacum L.) leaves. Parallel to the progression of leaf senescence, an increase in cytosolic GS polypeptides was detected in the mesophyll cytosol of senescing leaves while a significant decrease in GS protein content was observed in the phloem companion cells. The presence of GS polypeptides in the leaf cytosol of senescing leaves appears to be the result of an induction of the Gln1-3 gene, the transcripts of which are not detected in mature leaves but are abundant in senescing leaves. Alltogether, our results suggest that during senescence, ammonia assimilation is progressively shifted from the chloroplasts to the cytosol of leaf mesophyll cells.

The dual function of sugar carriers. Transport and sugar sensing

Sucrose and its derivatives represent the major transport forms of photosynthetically assimilated carbon in plants. Sucrose synthesized in green leaves is exported via the phloem, the long-distance distribution network for assimilates, to supply nonphotosynthetic organs with energy and carbon

Sucrose Transport in Higher Plants

Presumably due to its physicochemical properties, sucrose represents the major transport form of photosynthetically assimilated carbohydrates in plants. Sucrose synthesized in green leaves is transported via the phloem, the long distance distribution network for assimilates in order to supply nonphotosynthetic organs with energy and carbon skeletons. At least in Solanaceae, sugar export seems to be a tightly regulated process involving a number of specific plasma membrane proteins. Significant progress in this field was made possible by the recent identification of plasma membrane sucrose transporter genes. These carriers represent important parts of the long-distance transport machinery and can serve as a starting point to obtain a complete picture of long-distance sucrose transport in plants. A combination of biochemical studies of transporter properties together with expression and localization studies allow specific functions to be assigned to the individual proteins. Furthermore, the use of transgenic plants specifically impaired in sucrose transporter expression has provided strong evidence that SUT1 transporter function is required for phloem loading. Physiological analyses of these plants demonstrate that sucrose transporters are essential components of the sucrose translocation pathway at least in potato and tobacco.

Reduced sulphur allocation from three-year-old needles of Norway spruce (Picea abies[Karst] L.)

The 35 S-labelled sulphur compounds glutathione, cysteine, and γ-glutamylcysteine were fed to 6-year-old spruce trees via the cut surface of a single 3-year-old needle. After 1-3 h exposure, uptake of the radiotracer into the fed needle, export into other parts of the plant and distribution between needles, bark and wood along the transport path were analysed. Uptake of cysteine into the exposed needle was one order of magnitude and uptake of γ-glutamylcysteine two orders of magnitude lower than that of glutathione. Independent of the thiol applied, the current year's sprouts were the preferential sinks of exported 35 S. Transport towards basipetal parts of the twig amounted to less than 10% of total 35 S export in all cases. After feeding 35 S-cysteine and 35S-y-glutamylcysteine, 35 S-glutathione was found along the transport path, in particular in distant parts of the twig. This was also observed when 35 S-GSH was fed. This result confirms the significance of glutathione as the major long-distance transport form of reduced sulphur in spruce twigs. In xylem sap of trunk sections of spruce, cysteine rather than glutathione was the main thiol. Cysteine concentrations in the xylem sap of the trunk amounted to 260-500 nmol l -1 . Glutathione concentrations were 2-5 times and γ-glutamylcysteine concentrations 4-16 times lower than those of cysteine.

Inhibition of Human Glutathione Reductase by S‐nitrosoglutathione

S-Nitrosoglutathione (GSNO) represents a major transport form in nitric oxide (NO) in biological systems. Since NO and GSNO have been shown to modulate the function of various proteins, we studied the influence of GSNO and other NO donors on human glutathione reductase (GR). Catalyzing the reaction NADPH+GSSG+H(+)-->NADP(+) + 2 GSH, the dimeric flavoprotein GR is the central enzyme of the glutathione redox metabolism. GSNO was found to inhibit crystalline erythrocyte GR in two ways: (a) as a reversible inhibitor GSNO is competitive with glutathione disulfide (GSSG), the Ki being appr. 0.5 mM; (b) as an irreversible inhibitor; after 1 h (3 h) incubation with 1 mM GSNO, GR (2.5 U/ml, representing intraerythrocytic concentrations) was inhibited by 70% (90%). This inhibition depended on the presence of NADPH and could not be reversed by dilution nor by reducing agents. Absorption spectra indicate that the charge-transfer interaction between Cys63 and the flavin is abolished by this modification. In a GR sample inhibited by 90% with GSNO, the Km values for the substrates GSSG and NADPH were not significantly changed nor did the modification induce oxidase activity of the enzyme. GSNO was found not to be a substrate in the forward reaction of GR. This implies that GSNO is not accounted for by methods which employ GR for determining total glutathione. Incubating isolated GR for 60 min with other NO donors, namely 1 mM sodium nitroprusside or 1 mM S-nitroso-N-acetyl-DL-penicillamine (SNAP), resulted in only 25% and 10% inhibition, respectively. This attests to a specific affinity of GSNO to the enzyme. GSNO inhibition patterns comparable to purified authentic GR were obtained for purified recombinant GR, a GR mutant lacking the 15 N-terminal amino acids including Cys2, and for the enzyme present in diluted fresh haemolysates (0.02 U/ml); in concentrated haemolysates the inhibition was less pronounced. GR of intact erythrocytes was not affected when exposed to GSNO in the medium. Our results suggest that the irreversible inhibition of GR by GSNO involves nitrosylation of Cys63 and/or Cys58 at the catalytic site of the enzyme. To further investigate the mechanism of inactivation we have crystallized GSNO-modified GR for X-ray diffraction analysis.

Metabolic activation of the N-hydroxy derivative of the carcinogen 4-aminobiphenyl by human tissue sulfotransferases.

The role of human sulfotransferase(s) in the bioactivation of the N-hydroxy (N-OH) metabolite of the human bladder carcinogen 4-aminobiphenyl (ABP) was investigated in vitro with human tissue cytosols. Using an enzymatic assay consisting of a PAPS-regenerating system, [3H]N-OH-ABP, calf thymus DNA and tissue cytosols, the sulfotransferase-mediated metabolic activation of N-OH-ABP was determined as the PAPS-dependent covalent binding of the N-OH substrate to DNA. With cytosols prepared from various tissues, we found that the sulfotransferase(s) in human liver, and to a lesser extent colon, can readily metabolize N-OH-ABP. No PAPS-dependent metabolic activation was detected with cytosols prepared from human pancreas or from the carcinogen target tissue, the urinary bladder epithelium. The N-OH-ABP sulfotransferase activities of liver and colon cytosols from different individuals were highly correlated with their thermostable phenol sulfotransferase (TS-PST) activity (liver, r = 0.99, P < 0.01; colon, r = 0.88, P < 0.01), but not with activities for the thermolabile phenol sulfotransferase (TL-PST; liver, r = 0.29; colon, r = 0.53), or for the dehydroepiandrosterone sulfotransferase (DHEA-ST; liver, r = 0.32; colon, negligible activity). N-OH-ABP sulfotransferase activity was highly sensitive to inhibition by a selective TS-PST inhibitor, 2,6-dichloro-4-nitrophenol (IC50 = 0.7 microM), and by p-nitrophenol, but was unaffected by competitive inhibitors of TL-PST (dopamine) or DHEA-ST (DHEA, DHEA-sulfate). The N-OH-ABP sulfotransferase activity also exhibited thermostability properties similar to that of the TS-PST. From these data, we conclude that human liver TS-PST but not TL-PST or DHEA-ST can metabolically activate the proximate human carcinogen N-OH-ABP to a reactive sulfuric acid ester intermediate that binds covalently to DNA. In addition, in view of the putative role of N-OH-ABP as a major transport form of the carcinogen to the urinary bladder and of the absence of sulfotransferase activity in this tissue, we hypothesize that sulfotransferase activation in the liver may actually decrease the bioavailability of N-OH-ABP toward extrahepatic tissues and thus serve as an important overall detoxification mechanism for the urinary bladder.

Hepatic glutaminase expression: relationship to kidney-type glutaminase and to the urea cycle.

Glutamine functions as a major transport form of nitrogen and carbon within the body. In the liver, glutamine is hydrolyzed by a unique liver-type, phosphate-activated glutaminase, and the end products of hepatic glutamine catabolism are glucose and urea. Other tissues possess a different, kidney-type, glutaminase isozyme. The predicted amino acid sequences for the two glutaminases show a high degree of identity, indicating that they are products of different but related genes. Hepatic glutaminase activity is increased during diabetes, starvation, and on feeding high-protein diets, and decreased on feeding low-protein diets, whereas renal glutaminase appears to be regulated only by changes in acid-base status. Changes in the rate of gene transcription are the principal mechanism responsible for the long-term regulation of hepatic glutaminase, but the renal enzyme is regulated at the level of mRNA turnover. The pattern of regulation of hepatic glutaminase parallels that seen for genes encoding key enzymes of gluconeogenesis and urea synthesis, and indicates coordinate regulation of expression in keeping with the role of hepatic glutamine catabolism in these pathways.

Differential expression of two related amino acid transporters with differing substrate specificity in Arabidopsis thaliana

A general amino acid permease cDNA (AAP2) was isolated from Arabidopsis by complementation of a yeast mutant defective in citrulline uptake. Direct transport measurements in yeast show that the protein mediates uptake of L-[14C]-citrulline and L-[14C]-proline. Detailed analyses of the substrate specificity by competition studies demonstrate that all proteogenic amino acids are recognized by the carrier, including those that represent the major transport forms of reduced nitrogen in many species, i.e. glutamine, glutamate and asparagine. Thus, AAP2 is less selective as compared with AAP1 and transports basic amino acids such as histidine as shown by expression in a histidine transport-deficient yeast strain. The predicted polypeptide of 53 kDa is highly hydrophobic with 12 putative membrane-spanning regions and shows significant homologies to the Arabidopsis broad specificity permease AAP1, and a limited homology to bacterial branched chain amino acid transporters, but not to any other known proteins. Alterations in the charged residues as compared with AAP1 in four regions might be involved in the difference in selectivity towards basic amino acids. Both genes are highly expressed in developing pods indicating a role in supplying the developing seeds with reduced nitrogen. AAP2 is selectively expressed in the stem and might therefore play a role in xylem-to-phloem transfer of amino acids during seed filling. Furthermore in situ hybridization shows that both genes are expressed in the vascular system of cotyledons in developing seedlings.

Potato sucrose transporter expression in minor veins indicates a role in phloem loading.

The major transport form of assimilates in most plants is sucrose. Translocation from the mesophyll into the phloem for long-distance transport is assumed to be carrier mediated in many species. A sucrose transporter cDNA was isolated from potato by complementation of a yeast strain that is unable to grow on sucrose because of the absence of an endogenous sucrose uptake system and the lack of a secreted invertase. The deduced amino acid sequence of the potato sucrose transporter gene StSUT1 is highly hydrophobic and is 68% identical to the spinach sucrose transporter SoSUT1 (pS21). In yeast, the sensitivity of sucrose transport to protonophores and to an increase in pH is consistent with an active proton cotransport mechanism. Substrate specificity and inhibition by protein modifiers are similar to results obtained for sucrose transport into protoplasts and plasma membrane vesicles and for the spinach transporter, with the exception of a reduction in maltose affinity. RNA gel blot analysis shows that the StSUT1 gene is highly expressed in mature leaves, whereas stem and sink tissues, such as developing leaves, show only low expression. RNA in situ hybridization studies show that the transporter gene is expressed specifically in the phloem. Both the properties and the expression pattern are consistent with a function of the sucrose transporter protein in phloem loading.

Study of an underground physical distribution system in a high-density, built-up area

Abstract Urban environmental problems are becoming increasingly serious, as a result of traffic congestion and air pollution associated with the unipolar concentration of the population in large cities. Tokyo is a prime example of such an area. A study group concerned with urban environmental problems, focusing on physical distribution systems, has been discussing ways to improve the urban environment by creating new physical distribution systems that would replace automobiles as the major form of transportation used. The systems are based on the concept of “people aboveground, and commodities under ground”. This paper discusses the basic operational methods, cost-effectiveness, impact on society, and problems involved in the introduction of new systems for urban physical distribution. The east and west sides of Tokyo's Shinjuku Station are used as a model area.

Properties of Allantoinase From Whole Developing Fruits of French Bean, Phaseolus vulgaris L

In ureide-transporting legumes such as French bean, Phaseolus vulgaris L., allantoin is a major transport form of biologically fixed nitrogen. Allantoinase (allantoin amidohydrolase, EC 3.5.2.5) catalyses the conversion of allantoin to allantoate. In developing French bean fruits, seed coats contained the highest levels of soluble activity on a fresh weight basis, suggesting that this organ may be important in ureide metabolism. However, over 70% of the total allantoinase activity of the developing fruit was in the pods. Allantoinase from whole developing French bean fruits was partially purified and characterised. Dithiothreitol inhibited activity, suggesting that disulfide bridges are necessary for activity. Mn2+ was found to relieve this inhibition to some extent; however, the presence of Mn2+ or EDTA in incubation mixtures did not affect activity. This suggests that, whilst allantoinase may not be a metalloenzyme, Mn2+ may have a role in maintaining the structure of the active enzyme. The Km for allantoin was determined to be 40.3 mM and the molecular mass of allantoinase was 50 000. Acid pretreatment of a crude extract reduced activity to 82% of control activity. On the basis of sucrose density fractionation of French bean fruit extracts, allantoinase was determined to be associated with the microsomal fraction of the cell, probably the endoplasmic reticulum, as activity was coincident with NADPH-cytochrome c reductase.

Effects of aldehyde dehydrogenase inhibitors on the ex vivo sensitivity of murine late spleen colony-forming cells (day-12 CFU-S) and hematopoietic repopulating cells to mafosfamide (ASTA Z 7557)

The effects of inhibitors of aldehyde dehydrogenase activity on the sensitivity of murine pluripotent hematopoietic stem cells to oxazaphosphorine anticancer agents, e.g. mafosfamide, were examined using two different assay procedures. In the first part of the investigation, the ex vivo sensitivity of murine day-12 spleen colony-forming cells (CFU-S) to mafosfamide was determined in the absence and presence of known inhibitors of aldehyde dehydrogenase activity, viz. diethyldithiocarbamate and cyanamide. These results were compared to those generated for day-8 CFU-S. Day-12 CFU-S were less sensitive to mafosfamide, and to phosphoramide mustard, although the difference in sensitivity to the latter was less marked. Diethyldithiocarbamate and cyanamide each potentiated the cytotoxic action of mafosfamide toward both day-12 and day-8 CFU-S; they did not potentiate the cytotoxic action of phosphoramide mustard toward these cells. Since cellular aldehyde dehydrogenases are known to catalyze the oxidation of 4-hydroxycyclophosphamide/aldophosphamide, the major transport form of mafosfamide, to the relatively nontoxic acid, carboxyphosphamide, the results suggest that intracellular aldehyde dehydrogenase activity is a determinant of the sensitivity of day-12 CFU-S, as well as of day-8 CFU-S, to mafosfamide and other oxazaphosphorines, e.g. cyclophosphamide. In the second part of this investigation, a murine syngeneic bone marrow transplantation model was used to determine the ex vivo sensitivity of murine hematopoietic repopulating cells to mafosfamide in the absence and presence of diethyldithiocarbamate. Specifically, the ability of treated marrow grafts to repopulate the hematopoietic system, and thereby save recipients from the otherwise lethal effect of total body irradiation, was determined. Diethyldithiocarbamate potentiated the cytotoxic action of mafosfamide, but not that of phosphoramide mustard, toward hematopoietic repopulating cells. These observations support our previous contention that aldehyde dehydrogenase activity is an operative determinant with regard to the sensitivity of murine pluripotent hematopoietic stem cells to oxazaphosphorines.

Antigenic Similarity in Urate Oxidases of Major Ureide Producing Legumes and Its Correlation with the Type of Peroxisome in Uninfected Cells of Nodules

Dept. oj Biology, McGill University, Montreal, Quebec, Canada H3A 1B1Structural, biochemical and immunologica, l comparison of noduless fro temnspecies of plant s were mad to determine ief a correlation exists between nodulestructure, ureide production, urate oxidas ane activityd antigenic, similarit iyn urateoxidase. I specien s with high urate oxidase activit and cross-reactioy n with soybeananti-urate oxidase [soybea (Glycinen max), green bea (Phaseolusn vulgaris), mung bean(Vigna radiata), cowpe (Vignaa unguiculaia)], the nodules were determinate and containednumerous interstitial cells, th intersperse infectee d cellsd th amon.e Withig ninterstitial cells of the ureide producing nodules numerous peroxisomes were note anddthese peroxisomes appea to bre structurally similar viz, . a larg e electron opaque coresurrounded by a less electron opaqu rime . Although hem (Sesbaniap sesbani exaltata)anodules were simila irn ultrastructure to other ureide producers with detectable urateoxidase activity no cross-reactivit, way observes d with anti-soybean urate oxidase.Amide producing nodules either containe no interstitiad l cell [e.gs India. n jointvetch(Aeschynomene indica), showy crotalari (Crotalariaa spectabilis)} or interstitial cells with fewperoxisomes [e.g alfalf. a (Medicago saliva), broad bean (Viciafaba), pea (Pisum sativum)]with little urate oxidase activity, exhibitin no cross-reactiog n with soybean anti-urateoxidase. These data indicat the urate thae oxidast e in most ureide producing nodulesis very simila and structurally,r , ureide producin ar organizee ingd nodulesa specialize wad y to carry out ureide assimilatio inn the uninfecte d interstitial cells.Key words: Amid — Nodule e — Peroxisome — Ureide — Urate oxidase.Ureides are a major transport form of nitrogen in many nitrogen-fixing legumes:Prominent peroxisomes in uninfected interstitial cells of soybean (filycine max) nodules were firstnoted by Marks and Sprent (1974). They localized catalase (the peroxisomal marker enzyme)cytochemically, as further proof that they were indeed peroxisomes. Newcomb and Tandon(1981) hypothesized that these peroxisomes may be involved in ureide metabolism and that thepresence of prominent peroxisomes in interstitial cells could be used as a reliable indicator ofa ureide producer. This was confirmed in the case of soybean by cell fractionation, cytochemical,and immunocytochemical studies that indicated the presence of urate oxidase, a key enzyme inureide metabolism, in the nodule peroxisomes (Hanks et al. 1981, Vaughn et al. 1982, Nguyen etal. 1985). Work by Verma and colleagues (Legocki and Verma 1979, Bergmann et al. 1983)have shown that this nodule urate oxidase is a nodule-specific protein, a nodulin, and the geneencoding this enzyme has been isolated (Nguyen et al. 1985). Vaughn et al. (1982) and Shelp etAbbreviations: CAPS, cyclohexylaminopropane sulfonic acid; PVPP, polyvinylpolypyrrolidone.