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  • 1
    ISSN: 1432-072X
    Keywords: Regulation ; Fatty Acids ; Acinetobacter Species ; Neutral Lipids ; Phospholipids ; Turnover ; Hydrocarbons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 1. The regulation of fatty acid biosynthesis was studied inAcinetobacter strainHOl-N, a microorganism which grows on long chain paraffinic hydrocarbons. Dual-label experiments with acetate-3H and palmitate-1-14C were designed to assess the differences in fatty acid metabolism between hexadecane-and acetategrown cells: 2. Experiments involving non-growing conditions indicated a preferential labeling of the cellular lipids with acetate-3H in acetate-grown cells and palmitate-1-14C in hexadecane grown cells. In addition to this relationship, non-growing cells assimilated exogenous lipid precursors (acetate) or preformed lipid (palmitate) almost exclusively into the cellular neutral lipids. 3. Under growing conditions acetate-grown cells exhibited a transfer of lipid radioactivity from the neutral lipid fraction to the phospholipid fraction. 4. Hexadecane-grown cells preferentially labeled with palmitate-1-14C in the cellular lipid exhibited a 98–100% loss of neutral lipid radioactivity. 5. Palmitate derived directly from hexadecane oxidation diluted the radioactive free fatty acid pool 4 times faster in hexadecane-grown cells than in acetate-grown cells. 6. These results indicate that cells grown at the expense of hexadecane are characterized by mechanisms more efficient in the transport and assimilation of exogenous fatty acid and thatde novo fatty acid biosynthesis is significantly reduced in hexadecane-grown cells.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: Marine Bacterium ; Regulation ; Extracellular Enzymes ; Aminopeptidase ; Endopeptidase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A highly proteolytic Gram-negative, rod-shaped bacterium was isolated from the gills of fresh plaice and the effect of culture conditions on the production of proteolytic enzymes was investigated. When the organism, strain SA 1, was grown in the presence of complex mixtures of proteins and amino acids, both endopeptidase and aminopeptidase activity was demonstrated in the cell-free culture medium. However, synthesis of these enzymes was not observed when the organism was grown in a mineral medium with lactate or succinate as the only carbon and energy source. Synthesis of both endopeptidase and aminopeptidase was induced by the presence of amino acids in the medium. Of the amino acids tested, l-phenylalanine was found to be the best single inducer for the production of endopeptidase. When in addition one or more different amino acids were added, endopeptidase production was found to increase with increasing complexity of the mixture, up to a maximum which was obtained with five different amino acids. Production of the aminopeptidase was optimal when l-glutamic acid was used as a single inducer. For this enzyme the amount of enzyme activity released in the medium decreased with increasing complexity of the amino acid mixture. Endopeptidase as well as aminopeptidase activity was found to accumulate in the medium at the end of the logarithmic growth phase, when the culture was no longer growing exponentially. When the stationary phase was reached, enzyme production stopped. Production of both enzymes was immediately halted upon addition of chloramphenicol and was found to be repressed by glucose and lactate. These results suggest that synthesis of proteolytic extracellular enzymes by the organism studied is controlled by an efficient regulatory mechanism, in which growth rate is an important parameter.
    Type of Medium: Electronic Resource
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