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[Prev] | [Next]The periplasm is found in gram-negative bacteria and is the space in between the cytoplasmic and outer membranes. (Many feel a periplasm is also present in gram-positive bacteria in between the cytoplasmic membrane and the peptidoglycan.) The periplasm is filled with water and proteins and is therefore somewhat reminiscent of the cytoplasm. However, pools of small molecules in the periplasm are not like those in the cytoplasm because the membrane prevents the free exchange between these two compartments. Also, the proteins found in the periplasm are distinct from those in the cytoplasm and are specifically guided to this site during translation through specific signal sequences typically near their N-termini. Figure 2-64 lists some examples of these proteins.
The peptidoglycan shell that provides the strength to prokaryotic membranes is also found in the periplasmic space of gram-negative bacteria, while in gram-positive bacteria it provides the outside border to the periplasm.
| Enzyme Type | Examples | Function |
| Hydrolytic enzymes | phophatases | Degrading phosphate-containing compounds. |
| proteases | Degrading proteins and peptides. | |
| endonucleases | Degrading nucleic acids. | |
| Binding proteins | sugars, amino acids, norganic ions, vitamins | Binding substrates and docking with transport protein in membrane. |
| Chemoreceptors | Chemotaxis, ermination | Sensing the environment and changing cell behavior in response. |
| Detoxifying enzymes | β-lactamase | Degrading penicillin and related compounds before they get into the cell. |
Periplasmic enzymes have several main functions, detecting nutrients in the environment, degradation of polymers, and protection from harmful compounds.
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