Periplasmic space

The periplasmic space or periplasm is a space between the inner cytoplasmic membrane and external outer membrane of Gram-negative bacteria. It may constitute up to 40% of its total cell volume. The space contains a loose network of murein peptidoglycan chains, as well as a gel containing hydrolytic and degradative enzymes. Other enzymes in the gel are involved in various biochemical pathways including peptidoglycan synthesis, electron transport, and alteration of substances toxic to the cell (xenobiotic metabolism). In some species, the gel also contains beta-lactamase, an enzyme responsible for degrading penicillin. This can be of clinical importance when considering antibiotic resistance.

Since Gram-positive bacteria have no equivalent space, the enzymes they produce which would normally be retained in the periplasmic space of a Gram-negative bacterium are instead secreted into the external environment. These secreted enzymes are referred to as exoenzymes.

References

Further reading

• D. White, The Physiology and Biochemistry of Prokaryotes, Oxford University Press, Oxford, 2000, pp. 22.