Peptidoglycan is found in both Gram-negative and Gram-positive bacteria. It is present in larger amounts in Gram-positive bacteria as it appears as a multimolecular layer and can be found in association with additional compounds. In Gram-negative bacteria, it is found in either 1 or 2 layers between the inner and outer membrane.
Peptidoglycan is a macromolecule made up of alternating residues of N-acetyl-β-D-glucosamine (NAG) and N-acetylmuramic acid (NAM) joined together by a glycosidic bond. There is then a pentapeptide attached to the NAM amino acid which forms cross-links with other polysaccharide chains forming a 3D mesh-like layer. These cross-links are formed using the enzyme glycopeptide transpeptidase and provide peptidoglycan with stability. This stability allows it to provide mechanical support and prevent osmotic lysis from occurring in bacteria.
Penicillin inhibits the effect of peptidoglycan in bacteria by binding to serine in the enzyme glycopeptide transpeptidase. As a result, it can no longer catalyse the formation of cross-links. The enzyme is irreversibly inhibited which therefore results in the termination of bacterial growth.
Penicillin inhibits the transpeptidase linking together the polysaccharide chains and cells become osmotically sensitive and burst.
- ↑ http://www.chem.qmul.ac.uk/iupac/misc/glycp.html#3.9
- ↑ http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit1/prostruct/cw.html
- ↑ Berg J., Tymoczko J and Stryer L. (2012) Biochemistry, 7th edition, New York: WH Freeman: pg 252
- ↑ http://www.ncbi.nlm.nih.gov/books/NBK7986/