Biological properties of bacterial peptidoglycan.

Synthetic and natural muramyl peptides have a variety of biological actions in mammals, including the abilities to enhance sleep and body temperature. Although muramyl peptides can be detected constitutively in mammalian organisms, no biochemical synthetic pathways are known for muramyl peptides in mammals. However, muramyl peptides are well known as components of bacterial cell wall peptidoglycan (synonym: murein). Isolated bacterial cell walls elicit host responses similar to those produced by bacterial infections or by purified muramyl peptides. Mammalian cells which phagocytize bacteria can digest bacterial cell walls and release biologically active muramyl peptides. The released muramyl peptides then express some or all of the biological effects observed with synthetic muramyl peptides. Also, cell-free systems consisting of isolated bacterial cell walls and lysozyme produce substances with similar biological activities.