Cell Membrane Complex Research Articles

Ammonium Regulation in Aspergillus nidulans

l-Glutamate uptake, thiourea uptake, and methylammonium uptake and the intracellular ammonium concentration were measured in wild-type and mutant cells of Aspergillus nidulans held in various concentrations of ammonium and urea. The levels of l-glutamate uptake, thiourea uptake, nitrate reductase, and hypoxanthine dehydrogenase activity are determined by the extracellular ammonium concentration. The level of methylammonium uptake is determined by the intracellular ammonium concentration. The uptake and enzyme characteristics of the ammonium-derepressed mutants, meaA8, meaB6, DER3, amrA1, xprD1, and gdhA1, are described. The gdhA mutants lack normal nicotinamide adenine dinucleotide phosphate-glutamate dehydrogenase (NADP-GDH) activity and are derepressed with respect to both external and internal ammonium. The other mutant classes are derepressed only with respect to external ammonium. The mutants meaA8, DER3, amrA1, and xprD1 have low levels of one or more of the l-glutamate, thiourea, and methylammonium uptake systems. A model for ammonium regulation in A. nidulans is put forward which suggests: (i) NADP-GDH located in the cell membrane complexes with extracellular ammonium. This first regulatory complex determines the level of l-glutamate uptake, thiourea uptake, nitrate reductase, and xanthine dehydrogenase by repression or inhibition, or both. (ii) NADP-GDH also complexes with intracellular ammonium. This second and different form of regulatory complex determines the level of methylammonium uptake by repression or inhibition, or both.

Ammonium Regulation in Aspergillus nidulans

Conference Article| May 01 1973 Ammonium Regulation in Aspergillus nidulans J. A. PATEMAN; J. A. PATEMAN 1Department of Genetics, University of Glasgow, Glasgow G11 5JS, U.K. Search for other works by this author on: This Site PubMed Google Scholar J. R. KINGHORN; J. R. KINGHORN 1Department of Genetics, University of Glasgow, Glasgow G11 5JS, U.K. Search for other works by this author on: This Site PubMed Google Scholar ETTA DUNN; ETTA DUNN 1Department of Genetics, University of Glasgow, Glasgow G11 5JS, U.K. Search for other works by this author on: This Site PubMed Google Scholar E. FORBES E. FORBES 1Department of Genetics, University of Glasgow, Glasgow G11 5JS, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1973) 1 (3): 674–675. https://doi.org/10.1042/bst0010674 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation J. A. PATEMAN, J. R. KINGHORN, ETTA DUNN, E. FORBES; Ammonium Regulation in Aspergillus nidulans. Biochem Soc Trans 1 May 1973; 1 (3): 674–675. doi: https://doi.org/10.1042/bst0010674 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1973 Biochemical Society1973 Article PDF first page preview Close Modal You do not currently have access to this content.

Deoxyribonucleic acid synthesis in bacteriophage SPO1-infected Bacillus subtilis. I. Bacteriophage deoxyribonucleic acid synthesis and fate of host deoxyribonucleic acid in normal and polymerase-deficient strains.

The effect of bacteriophage SPO1 infection of Bacillus subtilis and a deoxyribonucleic acid (DNA) polymerase-deficient (pol(-)) mutant of this microorganism on the synthesis of DNA has been examined. Soon after infection, the incorporation of deoxyribonucleoside triphosphates into acid-insoluble material by cell lysates was greatly reduced. This inhibition of host DNA synthesis was not a result of host chromosome degradation nor did it appear to be due to the induction of thymidine triphosphate nucleotidohydrolase. Examination of the host chromosome for genetic linkage throughout the lytic cycle indicated that no extensive degradation occurred. After the inhibition of host DNA synthesis, a new polymerase activity arose which directed the synthesis of phage DNA. This new activity required deoxyribonucleoside triphosphates as substrates, Mg(2+) ions, and a sulfhydryl reducing agent, and it was stimulated in the presence of adenosine triphosphate. The phage DNA polymerase, like that of its host, was associated with a fast-sedimenting cell membrane complex. The pol(-) mutation had no effect on the synthesis of phage DNA or production of mature phage particles.

The Chemical Composition of Wool X. Material Digested by Trypsin From Fibres and Cortical Cells

Samples of wool, wool pretreated with formic acid, and cortical cells produced by mechanical agitation in formic acid have been digested by trypsin. The evidence shows that the formic acid treatment is not degradative. It is found by electron microscopy that trypsin digests the endocuticle, part of the cell membrane complex, and the nuclear remnants and intermacrofibrillar material of the. cortex. These digested components amount to about 3�6, 1� 8, and 12�6% by weight of the fibre respectively.

The Discontinuous Nature of Epicuticle on the Surface of Keratin Fibers

There has been considerable controversy over the question of whether the epicuticle forms a continuous outer sheath on keratin fibers or surrounds each cuticle cell individually. The evidence advanced by earlier workers in support of the former concept is reassessed critically and reinterpreted in other ways. At the same time, the formation of Allwörden sacs on isolated cuticle cells and other results show that the latter concept is correct, viz, that the epicuticle surrounds each cell individually and, hence, forms part of the cell membrane complex.

The Chemical Composition of Wool V. The Epicuticle

The cuticle membranes of wool raised by chlorine (epicuticle) and by bromine have been isolated and their thicknesses determined by electron microscopy of gold-shadowed specimens. These were found to be 32�10 A and 140�40 A respectively. The epicuticle consists of 78% protein, 5% lipid, 4% ash, and a negligible amount of carbohydrate. Amino acid analyses of the epicuticle and the dissolved protein which fills the Allworden sacs show that (with the exception of glycine) those amino acids which are present in larger amount in the epicuticle than in the whole cuticle are present in smaller amount in the dissolved protein and vice versa. Furthermore, the amino acid composition of the epicuticle resembles that of the cuticle more closely than that of the protein from the cell membrane complex. This fact, together with its low lipid content, suggests that it may not originate from the cuticle cell membrane complex.

The Theory of Shrinkproofing of Wool: Part V: Electron and Light Microscopy of Wool Fibers after Chemical Treatments

Lincoln 36's top, subjected to ten different chemical treatments as described in previous publications of this series [4, 5], was examined by light and electron microscopy using replica and thin-sectioning techniques. The sectioning and staining technique proved useful in showing the extent of penetration of the fiber by the reagent. The more drastic treatments such as 5% sodium hydroxide in water, hydrogen peroxide (10 vol for 16 hr), and severe treatment with chlorine (16% on weight of wool) caused almost complete obliteration of cellular detail throughout the fiber. Milder oxidation treatments may not have destroyed cellular detail, but may have oxidized sufficient disulfide bonds to prevent the TGA-OsO4 staining procedure from staining the matrix, with the result that the fine structure of microfibrils and matrix in the cortex were not visible. Alternative section staining procedures utilizing permanganate or lead hydroxide were also useful. Modification of the cuticle was observed after every treatment which effected shrinkproofing; namely, acid chlorination, treatment with permonosulfuric acid, hydrogen peroxide, sodium hydroxide, and treatment with permanganate in saturated salt. Some treatments (ethanol extraction, for example) produced a marginal degree of shrinkproofing and showed a small amount of cuticle modification. Other treatments (with peracetic acid, for instance) did not modify the cuticle and did not effect shrinkproofing. Thus, the primary requirement for shrinkproofing by degradative chemical treatments is sufficient modification of the fiber cuticle. The chemical reaction by which cuticle modification (and thereby shrinkproofing) is brought about generally involves cystine, but with the use of ethanolic sodium hydroxide the major process is probably the removal of a wool wax constituent from the cell membrane complex beneath the cuticle. Although modification of the cortex by chemical reaction is undesirable from a practical point of view, it has only a secondary effect on the degree of shrinkproofing. Various methods of confining the reaction to the cuticle are discussed. In particular, it was found that sodium hydroxide in water penetrates throughout the fiber, whereas the reaction was limited to the cuticle by the use of sodium hydroxide in ethanol or in an aqueous solution saturated with salt. Similarly, reaction of the cortex occurred with permanganate in water (with no subsequent shrinkproofing), whereas the presence of salt limited the reaction to the cuticle, thus producing shrinkproofing. The correlation between cuticle modification (hence degree of shrinkproofing) and alteration of frictional coefficients was good in most cases, but the lack of correlation in a few cases emphasized the importance of a new approach to the measurement of frictional coefficients.