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 reffered to as a periplasm.