AN in ~ ISH NMR STDDY OF BACTERIAL CELL WALIS

have proved to be useful model systeDlS for studying hOIIt' the structure and function of cellular organelles are detezmined by the course of their biosynthesis. Although the sequence of the biochemical events leading to the assembly of cellular structural components determine to a large extent function and supramolecular structure, the physico­ chemical properties of the biopolymers themselves might also contribute to shape and function (1). Less is known about the in vivo physico­ chemical properties of biopolymers, than about their biosynthesis. An understanding of the three-dimensional structures and molecular dy­ namics of biopolymers is often required to bridge the gap between bio­ chemical information on the one hand, and the structure of a cellular organelle, as revealed by electron microscopy, on the ~er. An eXlI,IIIple is the expression of the morphogenetically dete:mined shapes of bacteria. 'l!1e shape of a bacterial cell is maintained by the rigid peptidoglycan layer in its cell wall (2). It was once believed that correlations could be made between the shapes of bacteria and the chemical ccmposi­ tion of the peptidoglycan layer ( 2). However, it has subsequently been demonstrated that bacteria with different shapes can have identical peptidoglycans and that mutant bacteria can revert fram spherical to rod foms without changing the chemical cCllllposition of the peptidoglycan layer ( 3,4 ). The organization and motional properties of the peptido­ glycan layer now appear to be the deteminents of cell shape. Measurements of the in vivo physical properties of the biopolymers found in cellular organelles'haVe proved extremely difficult in complex biological systems. Meas1lX'8mnts on isolated cellular CIDIIIpOneDts cannot always be relied upon, since changes in organization IIIld confo:mation occur during isolation. Among the biophysical techniques available for characterizing the conformation and dynamic properties of polymeric systems, nuclear' magnetic resonance spectroscopy is a pranising tool for probing the in vi YO physico-chemical properties of biopolymers. Nmr resonllllces originating from specific sites in a polymer can often be 439