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A n t o n i e van L e e u w e n h o e k
47 (1981)
The notion that symport of organic acids can occur with more than one proton (Ramos and
Kaback, 1977) has led Michels et al. (1979) to formulate the "energy recycling model", implicating
that microorganisms can gain metabolic energy from the excretion of metabolic end-products. This
model has now obtained a firm experimental basis (Otto et al., 1980a, b; Ten Brink, 1980).
FRIEDBERG, I., HELLINGWERF, K. J. and KONINGS, W. N. 1980. Regulation of alanine transport
by a membrane potential dependent gating effect in Rhodopseudomonas sphaeroides. - - Abstr.
13th FEBS Meeting, Jerusalem, Abstr. no. $5-P77.
HELLINGWERF, K. J., FRmDBERG,I., LOLKEMA,J. S., MICI~ELS,P. A. M. and KON~N~S, W. N. 1981.
Energy coupling of facilitated transport of inorganic ions in Rhodopseudomonas sphaeroides. - J. Bacteriol., submitted.
KON1NGS, W. N., HELLINGWERF, K. J. and ROB1LLARD, G. T. 1981. Transport across bacterial
membranes, p. 257-283. In S. L. Bonting and J. J. H. M. de Pont (eds), Membrane transport.
- - Elsevier, Amsterdam.
LANYI, J. K. and SILVERMAN, M. P. 1979. Gating effects in Halobacterium halobium membrane
transport. - - J. Biol. Chem. 254: 4750-4755.
MICI-~LS, P. A. M., M1CrtELS, J. P. J., BOONSTRA,J. and KONINGS, W. N. 3979. Generation of an
electrochemical proton gradient in bacteria by the excretion of metabolic end-products. - FEMS Microbiol. Lett. 5: 357-364.
NICOI~AY, K., LOLKEMA,J. S., HELLINGWERF,K. J., KAPTEIN, R. and KONINGS, W. N. 1981. Quantitative agreement between the values for the light-induced ApH in Rhodopseudomonas sphaeroides measured with automated-flow dialysis and 31P-NMR. - - FEBS Lett. 123: 319-323.
OTTO, R., HUGENHOLTZ, J., KONINGS, W. N. and VELDKAMt', H. 1980. Increase of molar growth
yield of Streptococcus cremoris for lactose as a consequence of lactate consumption by Pseudomonas stutzeri in mixed culture. - - FEMS Microbiol. Lett. 9: 85-88.
OTTO, R., SONNENBERG, A. S. M., VELDKAMP, H. and KON1NGS, W. N. 1980. Generation of an
eleclcrochemical proton gradient in Streptococcus cremoris by lactate efflux. - - Proc. Natl. Acad.
Sci USA 77: 5502-5506.
RAMOS, S. and KABACK,H. R. 1977. pH-Dependent changes in proton : substrate stoichiometries
during active transport in Escherichia coli membrane vesicles. - - Biochemistry 16: 4271-4275.
ROT~rENBER~, H. 1976. The driving force for proton(s)-metabolites cotransport in bacterial cells.
FEBS Lett. 66: 159-163.
TEN BRINK, B. and KONINGS, W. N. 1980. Generation of an electrochemical proton gradient by
lactate efflux in membrane vesicles of Escherichia coli. - - Eur. J. Biochem. 111: 59-66.
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Transport through the outer membrane
of gram-negative bacteria
BEN LUGTENBERG
Department o f Molecular Cell Biology an d Institute for Molecular Biology,
State University, Transistorium 3, Padualaan 8. 3584 C H Utrecht,
The Netherlands
The cell envelope of gram-negative bacteria contains at least three layers (i) the cytoplasmic or
inner membrane, (ii) the peptidoglycan layer and (iii) the outer membrane. A so-called periplasmic
space is located between the two membranes. It contains soluble proteins mainly involved in bin-
Antonie van Leeuwenhoek 47 (1981)
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ding of nutrients of in degradation of solutes to a form suitable for transport through the cytoplasmic membrane.
The outer membrane contains phospholipid, lipopolysaccharide (LPS) and proteins. In Enterobacteriaceae the lipids are arranged in a bilayer such that LPS is located exclusively in the outer
leaflet and phospholipid exclusively in the inner leaflet. It is assumed that in several non-enteric
gram-negative bacteria some phospholipid is also present in the outer monolayer. Most outer
membrane proteins span the lipid bilayer.
Considerations on permeation of solutes through the outer membrane should take into account
the hydrophobicity of the solute as defined by its solubility in an octanol-water system. Hydrophobic solutes like bile salts, detergents and many antibiotics can pass membranes by diffusion
through phospholipid bilayer regions. Because of the molecular make up of their outer membrane,
this so-called hydrophobic pathway does not exist in Enterobacteriaceae.
Most hydrophilic solutes pass the outer membrane of Enterobacteriaceae by a diffusion-like process through water-filled pores which act as a non-specific molecular sieve, permitting the permeation of hydrophilic solutes up to a molecular weight of about 600. These general pores consist of
trimers of peptidoglycan-associated proteins which require LPS for biological activity. In non-enteric gram-negative bacteria the pores permit the diffusion of much larger solutes but the rate of
permeation through these pores is much lower. If the general pores do not allow the permeation
of sufficient amounts of a certain nutrient, the cell is often able to synthesize new outer membrane
protein pores to overcome this problem. For example, protein e and the bacteriophage ~ receptor
are synthesized by cells growing under phosphate limitation and in the presence of maltose, respectively. These proteins form pores designed to facilitate the permeation of polyphosphate and maltodextrins, respectively. They also allow the permeation of small molecules. The bacteriophage T6
receptor protein forms a pore suited for the permeation of nucleosides. Limitation for ferric ions
results in the derepression of five outer membrane proteins from which three have been identified
as proteins specifically involved in the permeation of Fe 3+-ligand complexes, namely ferrichrome,
Fe 3+-enterochelin and Fe 3+ -citrate.
The physical mechanism for the regulation of glucose
transport in Escherichia coli
G. T.
ROBILLARD 1 AND W .
N.
KONINGS 2
l Department of Physical Chemistry, University of Groningen
Nijenborg 16, 9747 AG Groningen, The Netherlands,
2Department of Microbiology, University of Groningen,
Kerklaan 30, 9751 NN Haren, The Netherlands
The phosphoenolpyruvate-dependent phosphotransferase system (PTS) of E. coli couples the
transport of glucose and certain other hexoses to the hydrolysis of phosphoenolpyruvate (PEP)
via a series of phosphorylgroup transfer reactions
EI
PEP + H P r ~ P - H P r
.
FIII-EII.
+ Pyr
P-HPr + rlexoseout M~W?-rl~'r + Hexose-Pin