Periplasmic space
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The periplasmic space is the space seen between the plasma membrane and the outer membrane in the gram-negative bacteria. A smaller periplasmic space between the plasma membrane and the peptidoglycan layer (cell wall) may be observed in the gram-positive bacteria. Periplasmic space may be filled with a loose network of peptidoglycan and may constitute up to 40% of the total cell volume. This space is involved in various biochemical pathways including nutrient acquisition, synthesis of peptidoglycan, electron transport, and alteration of substances toxic to the cell. Gram-positive bacteria do not have as many periplasmic proteins compared to the gram-negative bacteria. Instead gram-positive bacteria secrete enzymes which would normally be found in the periplasmic space of the gram-negative bacteria. These secreted enzymes are referred to as exoenzymes. Substance that occupies the periplasmic space is referred to as a periplasm.
The periplasmic space is of particular clinical importance in that it is the site, in some species, that contains beta-lactamase, an enzyme responsible for degrading the penicillin group of antibiotic drugs, leading to penicillin resistance.
In some bacteria such as Cytophaga small rotating particles that are thought to be made of proteins are found in the periplasmic space, these particles rotate like ball bearings deriving energy from membrane potential or ATP which gives these bacteria their gliding ability.
