Periplasmic space is the area found between two permeable boundaries. Periplasmic space is found in Gram-negative bacteria, between the inner and the outer membranes, according to UniProt. In Gram-positive bacteria, the periplasmic space is smaller and found between the polymer outer shell and the inner membrane.
The periplasm contains proteins and water and can be compared to cytoplasm. However, small molecules present in the periplasm are unlike cytoplasm, as the membranes prevent free exchanges from happening between the two compartments. Proteins that are present in the periplasm are very different from cytoplasm, and they are guided during translation by specific signals. Periplasmic enzymes play roles in motility, degradation of other compounds and transport.