The periplasmic space is the space seen between the plasma membrane and the outer membrane in the Gram-negative bacteria. The substance that occupies the periplasmic space is referred to as periplasm. A very small periplasmic space between the plasma membrane and the peptidoglycan layer (cell wall) may be observed in the Gram-positive bacteria.[1] The archaean Ignicoccus, also possesses a particularly large periplasm, which contains membrane-bound vesicles and is enclosed by an outer membrane.[2]
The periplasmic space is a lot thicker in Gram negative bacteria. This space may be filled with a loose network of peptidoglycan and may constitute up to 40% of the total cell volume.[3] This space is involved in various biochemical pathways including nutrient acquisition, synthesis of peptidoglycan, electron transport, and alteration of substances toxic to the cell.[4] Gram-positive bacteria do not have as many periplasmic proteins compared to the Gram-negative bacteria.[4] Instead Gram-positive bacteria secrete enzymes which would normally be found in the periplasmic space of the Gram-negative bacteria. This secreted enzyme is referred to as an exoenzyme.[4]
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.
References
- D. White, The Physiology and Biochemistry of Prokaryotes, Oxford University Press, Oxford, 2000, pp. 22.
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