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  • Diffusion  (1)
  • Proline transport  (1)
  • 1995-1999  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Threonine diffusion and threonine transport in Corynebacterium glutamicum and their role in threonine production (1996)
    Springer
    Archives of microbiology 165 (1996), S. 48-54 
    Details
    ISSN: 1432-072X
    Keywords: Key words Amino acid transport ; Uptake ; Excretion ; Diffusion ; Threonine ; Corynebacterium glutamicum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transmembrane threonine fluxes (i.e., uptake, diffusion, and carrier-mediated excretion) all contribut-ing to threonine production by a recombinant strain of Corynebacterium glutamicum, were analyzed and quantitated. A threonine-uptake carrier that transports threonine in symport with sodium ions was identified. Under production conditions (i.e., when internal threonine is high), this uptake system catalyzed predominantly threonine/threonine exchange. Threonine export via the uptake system was excluded. Threonine efflux from the cells was shown to comprise both carrier-mediated excretion and passive diffusion. The latter process was analyzed after inhibition of all carrier-mediated fluxes. Threonine diffusion was found to proceed with a first-order rate constant of 0.003 min–1 or 0.004 μl min–1 (mg dry wt.)–1, which corresponds to a permeability of 8 × 10–10 cm s–1. According to this permeability, less than 10% of the efflux observed under optimal conditions takes place via diffusion, and more than 90% must result from the activity of the excretion carrier. In addition, the excretion carrier was identified by (1) inhibition of its activity by amino acid modifying reagents and (2) its dependence on metabolic energy in the form of the membrane potential. Activity of the excretion system depended on the membrane potential, but not on the presence of sodium ions. Threonine export in antiport against protons is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050295
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  • 2
    Electronic Resource
    Electronic Resource
    Isolation of the putP gene of Corynebacterium glutamicum and characterization of a low-affinity uptake system for compatible solutes (1997)
    Springer
    Archives of microbiology 168 (1997), S. 143-151 
    Details
    ISSN: 1432-072X
    Keywords: Key wordsCorynebacterium glutamicum ; PutP ; Proline transport ; Compatible solutes ; Osmoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Corynebacterium glutamicum accumulates the compatible solutes proline, glycine betaine, and ectoine under conditions of high osmolality. Uptake of proline is mediated by both a high-affinity and a low-affinity secondary transport system. The low-affinity uptake system also accepts glycine betaine and ectoine as substrates. In the present study, the gene encoding the high-affinity proline uptake system PutP was isolated by heterologous complementation of Escherichia coli mutant strain WG389, which lacks the transport systems BetT, PutP, ProP, and ProU and is unable to synthesize proline and glycine betaine. This gene (putP) encodes a protein of 524 amino acids that shares identity with the proline transport systems PutP of E. coli, Staphylococcus aureus, Salmonella typhimurium, Haemophilus influenzae, and Klebsiella pneumoniae. Functional studies of PutP synthesized in E. coli mutant strain MKH13, which also lacks the transport systems for compatible solutes and is unable to synthesize glycine betaine, revealed that this carrier system is not regulated by the external osmolality on the level of activity. K m values of 7.6 mM for proline and 1.3 mM for sodium as cotransported ion were determined. Deletion of the putP gene allowed the functional characterization of another proline uptake system with low affinity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050480
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    Paper (German National Licenses)
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