Verlag des Forschungszentrums Jülich
JUEL-3621
Upon osmotic downshock, the cells preferentially released compatible solutes such as
glycine betaine and proline. Release of lysine and glutamate was restricted and ATP
was totally retained. The cells maintained relative high cytoplasmic potassium
concentrations. Several results suggest that the efflux is channel mediated. First,
the efflux was extremely fast reaching an efflux rate of 6000 µmol × min-1 × g
dm-1 or higher. Second, efflux was insensitive to the addition of external substrate.
It was also unchanged after uncoupling by CCCP. A continuous decrease of external
osmolarity leads to a continuous efflux of compounds. This also effects the energetic
situation of the cells.
The existence of mechanosensitive channels in the cytoplasmic membranes of C.glutamicum
could be demonstrated using patch-clamp techniques. Fragments of the plasma membrane
were fused into giant liposomes. Application of suction in the pipette revealed the
presence of two types of high conductance mechanosensitive channels that were
voltage-independent and could be inhibited by gadolinium. Both channels were
characterized by their slow kinetics, their weak cationic selectivity, and differed
only by their conductance (600-700 pS and 1200-1300 pS in 0.1 M Kcl), raising the
possibility that they might correspond to different oligomers of the same subunit.
Since their discovery in bacteria it has been proposed that mechanosensitive
channels play a physiological role in sensing and/or adapting to changing osmotic
environments. The involvment of these channels in the shock-induced release of
compatible solutes in C.glutamicum is discussed.
Ruffert, Susanne
Funktion und Regulation mechanosensitiver Efflux-Systeme für kompatible Solute in Corynebacterium glutamicum
95 S., 1999
Under conditions of low osmolality cells are exposed to massive water influx.
In response to sudden hypoosmotic stress, the gram positive soil bacterium
Corynebacterium glutamicum releases low-molecular-mass solutes to maintain constant
turgor pressure. The systems that mediate the efflux process have been studied.
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