J. Biol. Chem., Vol. 255, Issue 11, 5075-5081, Jun, 1980
Different sidedness of functionally homologous essential thiols in two membrane-bound phosphotransferase enzymes of Escherichia coli detected by permeant and nonpermeant thiol reagents
R Haguenauer-Tsapis and A Kepes
The membrane-bound Enzyme IIbgl and IIglc are both inactivated in vivo by
the sulfhydryl reagent N-ethylmaleimide. The former is also inhibited by
the hydrophilic sulfhydryl reagents p-chloromercuribenzoic acid and
p-mercuriphenylsulfonic acid, while the latter is resistant to these
reagents. However, inhibition of this enzyme is observed after impairment,
either transient or permanent, of the permeability barrier of bacterial
envelopes. Since p-chloromercuribenzoic acid and p-
chloromercuriphenylsulfonic acid are able to cross the outer membrane of
Escherichia coli, their failure to inhibit in vivo Enzyme IIglc must be due
to their inability to cross the inner membrane of the bacteria. It would
therefore appear that sensitive thiol group(s) of Enzyme IIglc and Enzyme
IIbgl, in spite of their functional similarity, exhibit opposite
orientation within the cytoplasmic membrane, the first enzyme having an -SH
group accessible from the outer surface of the membrane, while the second
has an -SH group accessible from the inner surface of the membrane. The
present results strengthen the view that these two enzymes have in
asymmetric orientation within the membrane as already suggested by their
vectorial function.
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