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  • Life and Medical Sciences  (7)
  • 21.60.Ev  (1)
  • 1990-1994  (8)
  • 1
    ISSN: 1434-601X
    Keywords: 21.60.Ev ; 27.90.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Positive and negative parity bands have been followed up to 10+ (possibly 12+) and 11− in224Ra and are compared to the corresponding bands in the isotone226Th. If a constant value of the intrinsic quadrupole moment is assumed for allE2 transitions in224Ra theE1/E2 branching ratios are consistent with an intrinsic dipole moment of ¦Q1¦=0.032(3)e·fm. This small value, as compared to ¦Q1¦=0.30(2)e·fm for226Th, can be explained by an almost complete cancellation of large positive liquid-drop and negative shell-model contributions.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 27 (1994), S. 284-293 
    ISSN: 1059-910X
    Keywords: Mitochondrion ; Contact sites ; Protein translocation ; Ribosomes ; Import intermediates ; Receptor proteins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Mitochondrial protein targeting includes both intramitochondrial sorting of proteins encoded by the organellar genome and import and subsequent sorting of nuclear encoded precursor proteins. Only a few proteins are encoded by the mitochondrial genome and synthesized in the organellar matrix. These include predominantly inner membrane proteins that are perhaps co-translationally inserted into this membrane. Biochemical data suggest that insertion into the inner membrane may be confined to the inner boundary membrane. Ultrastructurally, however, a preferential association of ribosomes with either inner boundary or cristae membranes has not been established.The majority of the mitochondrial proteins are nuclear encoded and synthesized as precursors in the cytosol. Electron microscopic studies revealed that import of precursor proteins is generally confined to sites where both mitochondrial envelope membranes are closely apposed. In line with these observations, biochemical studies indicated that precursor proteins destined for the inner membrane or matrix have to interact with the energized inner membrane to allow complete passage of the precursor through the outer membrane. As a consequence, the mitochondrial envelope membranes have to be in close proximity at protein import sites.In isolated mitochondria distinct sites (designated as contact sites) exist where both envelope membranes are closely apposed and presumably stably associated. In situ, however, mitochondrial boundary membranes are in close proximity over large areas that cover almost the entire mitochondrial periphery. Consequently, the relative area of the mitochondrial surface, where both boundary membranes are in sufficient proximity for allowing protein translocation, is generally larger in situ compared to that in isolated organelles.Immunocytochemical localization studies showed a rather random distribution of components of the mitochondrial protein translocation machinery over the entire mitochondrial surface and not confined to contact sites.Based on these ultrastructral data and recent biochemical findings we propose that mitochondrial protein import sites are dynamic in nature and include relatively labile regions of close association of the boundary membranes. In vitro, however, mitochondrial protein import may preferentially take place at or near the presumably stable contact sites. © 1994 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 6 (1990), S. 87-97 
    ISSN: 0749-503X
    Keywords: Hansenula polymorpha ; methylotrophic yeast ; microbodies ; peroxisome-deficient mutants ; alcohol oxidase ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: As a first step in a genetic approach towards understanding peroxisome biogenesis and function, we have sought to isolate mutants of the methylotrophic yeast Hansenula polymorpha which are deficient in peroxisomes. A collection of 260 methanol-utilization-defective strains was isolated and screened for the ability to utilize a second compound, ethanol, the metabolism of which involves peroxisomes. Electron microscopical investigations of ultrathin sections of selected pleiotropic mutants revealed two strains which were completely devoid of peroxisomes. In both, different peroxisomal matrix enzymes were active but located in the cytosol; these included catalase, alcohol oxidase, malate synthase and isocitrate lyase.Subsequent backcrossing experiments revealed that for all crosses involving both strains, the methanol- and ethanol utilizing-deficient phenotypes segregated independently of each other, indicating that different gene mutations were responsible for these phenotypes. The phenotype of the backcrossed peroxisome-deficient derivates was identical: defective in the ability to utilize methanol but capable of growth on other carbon sources, including ethanol.The mutations complemented and therefore were recessive mutations in different genes.
    Additional Material: 6 Ill.
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  • 4
    ISSN: 0749-503X
    Keywords: Hansenula polymorpha ; alcohol oxidase ; amine oxidase ; choline ; peroxisome-deficient mutant ; enzyme assembly ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We have studied the expression of alcohol oxidase (AO) in a peroxisome-deficient mutant strain of Hansenula polymorpha. High levels of octameric, active AO (up to 3·0 U/mg protein) were detected in cells grown at low dilution rates in a glucose-limited chemostat in the presence of choline as the sole nitrogen source. Monomeric or other intermediate forms of AO were not detected in the mutant strain. This indicated that assembly of the protein into active octameric molecules in the cytosol was as efficient as in wild-type cells where this process is confined to the peroxisomal matrix. At relatively low rates of expression (less than 1 U/mg protein) AO was localized throughout the cytosol and, surprisingly, was also present inside the nucleus. However, at enhanced levels large crystalloids were formed. Generally one crystalloid was observed per cell, whereas smaller ones were occasionally found in developing buds. Also large crystalloids have been observed inside the nucleus. These crystalloids were not surrounded by a membrane. Based on the morphology of the molecules that constituted these crystalloids and the results of (immuno)cytochemical experiments we conclude that the crystalloids are composed of octameric AO molecules, arranged in a regular lattice, identical to the 3-dimensional architecture previously described for the crystalline matrix of peroxisomes in methanol-grown wild type cells of H. polymorpha. Attempts to purify the crystalloids by conventional fractionation methods failed, due to their apparent fragility; however, (immuno)cytochemical experiments revealed that catalase and dihydroxyacetone synthase were also associated with these structures.
    Additional Material: 15 Ill.
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  • 5
    ISSN: 0749-503X
    Keywords: Yeast ; Hansenula polymorpha ; microbodies ; biogenesis ; PER genes ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In the course of our studies on the molecular mechanisms involved in peroxisome biogenesis, we have isolated several mutants of the methylotrophic yeast Hansenula polymorpha impaired in the import of peroximal matrix proteins. These mutants are characterized by the presence of small intact peroxisomes, while the bulk of the peroxisomal matrix protein is not imported and resides in the cytosol (Pim- phenotype). Genetic analysis of back-crossed mutants revealed five different complementation groups, which were designated PERI-PER5. Mapping studies to determine the linkage relationships indicated that the observed Pim- phenotypes were determined by single recessive nuclear mutations.The different mutants had comparable phenotypes: (i) they were impaired to utilize methanol as the sole source of carbon and energy but grew well on various other compounds, including nitrogen sources, the metabolism of which is known to be mediated by peroxisome-borne enzymes in wild-type cells; (ii) all peroxisomal enzymes tested were induced, assembled and activated as in wild-type cells although their activities varied between the different representative mutants; (iii) all peroxisomal proteins, whether constitutive or inducible, were found both in the cytosol and in the small peroxisomes. These results suggest that a general, major import mechanism is affected in all mutants.
    Additional Material: 2 Ill.
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  • 6
    ISSN: 0749-503X
    Keywords: Peroxisomes ; oleic acid ; β-oxidation ; membrane proliferation ; Hansenula polymorpha ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We studied the physiological responses of Hansenula polymorpha during adaptation of cells to oleic acid-containing media. Growth experiments indicated that the organism was unable to use oleic acid as the sole source of carbon and energy. However, upon incubation of glucose-grown cells in mineral media containing oleic acid, activities of various enzymes of the β-oxidation pathway were induced. These enzymes were localized in microbodies together with alcohol oxidase. Furthermore, a drastic increase in phospholipid content of the cells was observed; this was due to a rapid proliferation of membranes. These consisted of a variable number of membranous layers which were continuous with the peroxisomal membrane. Upon continued incubation, the membrane proliferations extended and large compartments were formed. This process was dependent on the presence of peroxisomes in the cells since it was not observed in peroxisome-deficient mutant strains of H. polymorpha. The newly formed membranous compartments differed from peroxisomes since they did not contain peroxisomal matrix proteins; these were confined to the single enlarged organelle which was incorporated in the membranous structure and characterized by a large alcohol oxidase crystalloid. The membranous compartments are considered to be whole entities since they could not be separated from the peroxisomes by common cell fraction methods; also they were degraded entirely after a shift of cells to glucose-excess condition.Freeze fracturing reveled that the substructure of the membranes greatly resembled that of normal peroxisomal membranes. Since a distinct enhancement of different peroxisomal membrane proteins was observed during the initial hours after the shift, we assume that exposure of H. polymorpha to acid lead to a drastic overproduction of peroxisomal membranes.
    Additional Material: 12 Ill.
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  • 7
    ISSN: 0749-503X
    Keywords: Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Additional Material: 11 Ill.
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  • 8
    ISSN: 0749-503X
    Keywords: Hansenula polymorpha ; peroxisomes ; amine oxidase ; peroxisomal targeting signal ; homologous recombination ; integration ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Amine oxidase (AMO) is a peroxisomal matrix protein of Hansenula polymorpha, which is induced during growth of the yeast in media containing primary amines as a sole nitrogen source. The deduced amino acid sequence of the protein contains an SRL sequence at nine amino acids from the C-terminus. In this study, we have examined the possible role of the SRL motif in sorting of AMO to peroxisomes by mutating the corresponding gene sequence. For this purpose, we have developed a DNA construct that is specifically integrated into the AMO locus of the H. polymorpha genome, placing the mutant gene under the control of the endogenous AMO promoter and eliminating expression of the wild-type gene. Analysis of a stable transformant, containing the desired gene configuration, showed that mutation of the C-terminal sequence neither interfered with correct targeting of the protein into the peroxisome nor displayed significant effects on its activity. From this, it was concluded that the SRL-containing C-terminus is not essential for peroxisomal targeting of AMO in H. polymorpha.
    Additional Material: 5 Ill.
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