The chemical structure of the cell wall of Gram-positive bacteria
In the past, the role of organic chemistry has been to establish the structure of natural products, to duplicate these products, and synthesize infinite variations of them for the amelioration of our standard of living. Recently, however, organic chemistry, together with its derived disciplines biochemistry and molecular biology, has broadened in scope and has started to give us basic knowledge about biological processes. This knowledge is valid, however, only when it is based on chemical structures, the identification of which has been made by rigorous methods and eventually supported by synthetic proofs. This knowledge is valid, in other words, only when it is based on the same foundation as the chemistry of natural products has been based in the past. Most developments in the field of molecular biology have concerned proteins and nucleic acids. There are, however, biological phenomena (for example, the immunological protection of the cell, the duplication of the bacterial cell, and its penetration by viruses) in which carbohydrate structures play a major role. When we come to know the chemical structure of the rigid and insoluble component that gives form and protection to bacteria, we will better understand some important biological phenomena at the molecular level. To take two particularly interesting examples, we will be able to explain in chemical terms the penetration of viruses into the bacterial cell and also the action of antibiotics, such as penicillin, which block the formation of the cell wall. Only recently, moreover, has the spatial structure of egg-white lysozyme, one of the enzymes that cause the lysis of bacteria, been elucidated'. When we know completely the chemical structure of the lysozyme substrate, we will be in a position to explain the mechanism of enzyme action. In recent years, methods have been developed for the preparation of cell wall material devoid of cytoplasmic or membrane material, so that chemical methods may be applied to the purified material. Cell walls of grampositive bacteria were found to have, in general, a simpler composition than do cell walls of gram-negative bacteria, which have complex protein— lipopolysaccharidic antigens. We have to thank Salton, Work, Cummings, and Westphal, among others, for the pioneering work which determined the composition of bacterial cell walls. One of the first cell-wall structures to be studied was that of Micrococcus lysodeilcticus, which is the substrate traditionally used for the study of egg-white lysozyme. Taking advantage of the solubilization of the cell wall by the