Protein structure is obviously important to the understanding of a very large number of biochemical processes. However, proteins seldom act alone. They interact with substrates, receptors, and with one another to fine tune their activities and specificities. NMR offers the opportunity to not only determine structure (in solution for the cases of interest here) but to focus on particular regions involved in critical contacts. Isotope edited NMR experiments are a key component in allowing this focus. We have implemented a full array of these experiments and are applying them to interesting protein systems. One involves components of chaperonin systems important for protein folding. Another involves a lectin related to the carbohydrate receptor studies. Another involves components of multienzyme systems important in the synthesis and modification of long chain fatty acids.