Molecular cloning of the phosphate (inorganic) transport (pit) gene of Escherichia coli K12. Identification of the pit+ gene product and physical mapping of the pit-gor region of the chromosome

Summary The pit ⁺ gene, encoding the phosphate (inorganic) transport system of Escherichia coli, was isolated from a library of E. coli genes inserted in the cosmid vector pHC79. A 25.5-kb chromosomal DNA fragment was shown also to carry the gor locus encoding glutathione oxidoreductase. Physical mapping placed the two genes about 10 kb apart, confirming bacteriophage P1 mapping of the 77-min region. Subcloning and deletion analysis indicated that the entire pit ⁺ gene was located within a 2.2-kb Sal1-Ava1 fragment. The pit ⁺ gene product was identified by SDS-polyacrylamide gel electrophoresis as a 39-kdal inner membrane protein by two methods: (i) ³⁵S-methionine-labelling of minicells carrying pit ⁺ plasmids or plasmids from which all or part of the pit ⁺ gene was deleted. (ii) Overproduction of the Pit protein using a thermoinducible runaway replication plasmid.Complementation of the pit-1 mutant allele using a unit-copy-number pit ⁺ plasmid indicated that the pit-1 mutation is recessive.Strains carrying a multicopy pit ⁺ plasmid show a 10-fold increase in the initial rate of phosphate uptake; however there is no change in the steady-state level of ³²Pi accumulation.Abbreviations kb kilobase-pairs - kdal kilodalton - Pi inorganic phosphate - G3P sn-glycerol-3-phosphate - LB Luria broth - Tc tetracycline - Cm chloramphenicol - Ap ampicillin - UV ultraviolet light - TE 10 mM Tris.HCl, pH 8.0, 1 mM EDTA - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid     

The human hypothalamic LHRH precursor is the same size as that in rat and mouse hypothalamus

The synthesis of the decapeptide luteinizing hormone releasing hormone (LHRH) in human, rat and mouse brain has been investigated by studying the in vitro translation products of Poly A+ mRNA extracts from the hypothalamus. The translation products of all three species contained a single 28000 MW polypeptide which immunoprecipitated with a specific anti-LHRH serum. This polypeptide was not present in the translation products of Poly A+ mRNA extracts from the hypothalamus of the hypogonadal mouse, a mutant strain totally deficient in LHRH. These results show that in the human, rat and normal mouse, LHRH is synthesized as a component of a precursor peptide with a molecular weight of 28000.     

The distribution of NADPH-protochlorophyllide oxidoreductase in relation to chlorophyll accumulation along the barley leaf gradient

The possible regulatory role of NADPH-protochlorophyllide oxidoreductase for chlorophyll accumulation has been investigated in barley plants. Within the primary leaf of etiolated plants the different maturation stages of etioplasts are found in a linear series with the youngest in cells near the base and the oldest in cells near the tip. This distribution of different plastid forms is paralleled by drastic differences in the NADPH-protochlorophyllide-oxidoreductase content of the plastids and their capacity to accumulate chlorophyll during illumination. The amount of enzyme and the rate of chlorophyll accumulation are highest in the mature etioplast in the tip of the leaf and both decline rapidly with decreasing age of the leaf tissue, being almost undetectable in the leaf base. The translatable mRNA coding for the enzyme shows a different distribution pattern within the leaf. The highest concentration is found in the middle part of the leaf while in the top part only traces of this mRNA are detectable. It is concluded that during leaf development the enzyme is synthesized rapidly only during a limited time period and that it is stored subsequently in the mature etioplast as a stable protein. The close correlation between the distribution of the enzyme within the barley leaf and that of the potential to accumulate chlorophyll during illumination would favour a control of chlorophyll accumulation by the amount of NADPH-protochlorophyllide oxidoreductase. Dark-grown plants which were exposed to far-red light were used to test this possibility. The far-red-absorbing form of phytochrome (P_fr) has an inverse effect on the kinetics of chlorophyll accumulation and the enzyme concentration. Our results indicate that the rate of chlorophyll accumulation in barley is not determined by the level of NADPH-protochlorophyllide oxidoreductase present in the leaves.     

Effects of crop rotation and fertilization on catalase activity in a soil of the southeastern United States

Summary Catalase activity of a loamy sand under a 3-year crop rotation in the southeastern U.S.A. was monitored. Corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] were the summer crops in the rotation. Winter wheat (Triticum aestivum L.) was planted after corn, and soybean was followed by a winter fallow period. Cotton was followed by a mixture of common vetch (Vicia sativa L.) and crimson clover (Trifolium incarnatum Gibelli & Belli) which was eventually plow-incorporated as a green manure. Highest mean catalase activities were recorded in soil under the wheat, soybean, and winter legume crops; lowest activities were found in soil bearing corn and cotton, and during the winter fallow period. The fertilization regime influenced soil catalase activity independently of the crop. Soil deficient in any of the major elements showed low enzyme activity. Highest activity was found in soil fertilized with P and K, and with N supplied by a winter legume crop. Addition of supplementary mineral nitrogen to this regime reduced catalase activity. Elimination of the winter legume crop from an otherwise complete fertilization regime resulted in a drastic reduction in enzyme activity. In soil receiving a complete fertilization regime there was a close correlation between soil catalase and xylanase activities. A similar correlation between these two enzymes was not found in soil receiving incomplete fertilization.     

The role of thiosulfate in sulfur metabolism of Rhodopseudomonas globiformis

Rhodopseudomonas globiformis is able to assimilate both sulfur moieties of thiosulfate. During growth on ³⁵S-labelled thiosulfate the amino acids cysteine, homocysteine and methionine were labelled. The bulk of thiosulfate, however, was oxidized to tetrathionate and accumulated in the medium. A thiosulfate: acceptor oxidoreductase was partially purified and characterized. The enzyme oxidized thiosulfate to tetrathionate in the presence of ferricyanide. A c-type cytochrome isolated from this organism was reduced by this enzyme.     

Peroxidase-catalysed oxidation of chlorophyll by hydrogen peroxide

Chlorophyll is effectively bleached by H₂O₂ in the presence of certain phenols and peroxidase (EC 1.11.1.7) extracted from acetone powders of orange flavedo (Citrus sinensis). Optimal conditions for chlorophyll: hydrogen peroxide oxidoreductase include: pH, 5.9; [H₂O₂] 222 μM; ionic strength 0.11. A phenol is required and resorcinol is the most effective. Catechol and hydroquinone are inhibitory. Chlorophyll a, chlorophyllide a, and chlorophyll b all have similar V_max but K_m for chlorophyll a is about one-third that of chlorophyll b, while the K_m for chlorophyllide a is about one-half that of chlorophyll a. Pheophytin a was much less reactive than chlorophyll a, and Mg²⁺ included in the reaction system did not affect rates of pheophytin destruction.     

The Loss of In Vivo Activity of Recombinant Human Erythropoietin by Active Oxygen Species

The effects of active oxygen species on the in vivo activity of recombinant human erythropoietin (EPO) treated by Fenton system, xanthine (X) plus xanthine oxidase (XO) system and hydrogen peroxide (H₂O₂) has been studied by means of counting the increase in number of hemolyser-resistant cells (HRCs) in EPO-injected mice. The results showed that both Fenton and X plus XO systems caused a significant reduction of the activity in proportion to the concentration of generated active oxygen species. Meanwhile, the treatment of EPO with H₂O₂ alone resulted in a relatively slight reduction of the activity. Electrophoretic studies on the structure of EPO revealed that its main protein band on sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) disappeared in proportion with the extent of exposure to active oxygen generating systems. Both Fenton and X plus XO systems caused a significant loss of fluorescence in the pyridylamino (PA-) sugar chain in proportion to the concentration of generated active oxygen species, and no degradation products in the sugar chain part of the PA-sugar chain were detected. This showed that aromatic groups in EPO were sensitive to attack by active oxygen species. These results provide evidence that hydroxyl radical and other active oxygen species have a potential to react with EPO, leading to a reduction of its in vivo activity.     

EPR and Mössbauer spectroscopic studies on the tetrameric,NAD-linked hydrogenase of Nocardia opaca 1b and its two dimers: 1. The βδ-dimer—a prototype of a simple hydrogenase

The cytoplasmic, tetrameric NAD-linked hydrogenase from Nocardia opaca 1b can be separated in two dimeric substructures, an -dimer with NADH:electron acceptor oxidoreductase (diaphorase) activity and a -dimer which displays hydrogenase activity with artificial electron carriers. These two dimers were preparatively isolated by a FPLC Mono Q procedure in the absence of nickel and at alkaline pH values. The hydrogenase-active -dimer contained, as analyzed by inductively coupled plasma mass spectrometry (ICP-MS), 3.5–3.9 iron atoms and 1.3–1.7 nickel atoms per dimer molecule. EPR and Mössbauer spectra indicated the presence of a [4Fe-4S] cluster. This center turned out to be extremely labile towards oxidants. Oxidation led to irreversible convertion into a [3Fe-4S] form, thus representing an artifact and not a regulatory state of the cluster. The midpoint redox potential of the [4Fe-4S] cluster was determined to be -385 mV. Very weak EPR Ni signals of the -dimer were detectable in the oxidized as well as in the reduced state. The diaphorase-active -dimer was free of nickel and the iron content corresponded to 11.2–12.8 Fe atoms per dimer molecule. From EPR and Mössbauer measurements it was concluded that this dimer contained two [4Fe-4S] clusters, one [2Fe-2S] and one [3Fe-4S] cluster. In accordance with the results obtained for the dimer proteins, for the whole enzyme an iron content of 15.8–16.2 atoms per enzyme molecule have been determined. EPR spectra and spectrum simulations of the native hydrogenase corroborate the cluster assignments of the two dimers: in total the enzyme contains one [2Fe-2S] cluster, one [3Fe-4S] cluster and three [4Fe-4S] clusters.     

Mechanistic and phenomenological features of proton pumps in the respiratory chain of mitochondria

Various direct, indirect (kinetic and thermodynamic), and combined mechanisms have been proposed to explain the conversion of redox energy into a transmembrane protonmotive force (p) by enzymatic complexes of respiratory chains. The conceptual evolution of these models is examined. The characteristics of thermodynamic coupling between redox transitions of electron carriers and scalar proton transfer in cytochromec oxidase and its possible involvement in proton pumping is discussed. Other aspects dealt with in this paper are: (i) variability of H⁺/e ^– stoichiometries, in cytochromec oxidase and cytochromec reductase and its mechanistic implications; (ii) possible models by which the reduction of dioxygen to water at the binuclear heme-copper center of protonmotive oxidases can be directly involved in proton pumping. Finally a unifying concept for proton pumping by the redox complexes of respiratory chain is presented.     

Extracellular laccases and peroxidases from sycamore maple (Acer pseudoplatanus) cell-suspension cultures

We have investigated the abilities of extracellular enzymes from dark-grown cell-suspension cultures of sycamore maple (Acer pseudoplatanus L.) to oxidize monolignols, the precursors for lignin biosynthesis in plants, as well as a variety of other lignin-related compounds. Laccase and peroxidase both exist as a multiplicity of isoenzymes in filtrates of spent culture medium, but their abilities to produce water-insoluble, dehydrogenation polymers (DHPs) from the monolignols (in the presence of hydrogen peroxide for the peroxidase reaction) appear identical whether or not the enzymes are purified from the concentrated filtrates or left in a crude mixture. The patterns of bonds formed in these DHPs are identical to those found in DHPs synthesized using horseradish peroxidase or fungal laccase, and many of these bonds are found in the natural lignins extracted from different plant sources. On the other hand, sycamore maple laccase is very much less active on phenolic substrates containing multiple aromatic rings than is sycamore maple peroxidase. We suggst that whereas laccase may function during the early stages of lignification to polymerize monolignols into oligo-lignols, cell-wall peroxidases may function when H₂O₂ is produced during the later stages of xylem cell development or in response to environmental stresses.Abbreviations DHP dehydrogenation polymer - IEF isoelectric focuring - NMR nuclear magnetic resonance - PAGE polyacrylamide gel electrophoresis The authors wish to thank Dr. Masahiro Samejima (University of Tokyo) for provision of lignin model compounds and Dr. Göran Gellerstadt (Royal Institute of Technology, Sweden) for helpful suggestions regarding stilbene formation and light spectroscopy. Monolignols were prepared by Mr. Nate Weymouth with help from Dr. Herb Morrison (USDA/ARS, Richard B. Russell Research Center, Athens, GA). Thanks also to Ms. Izabella Poppe of the Complex Carbohydrate Research Center (CCRC) for assistance with carbohydrate analyses, and Mr. Vincent Sorrentino for help with the growth of cell-suspension cultures.