A survey of x-ray diffraction studies of enzyme-other molecule interactions as possible models for receptor sites.

In the absence of a structure for a hormone-receptor complex, one may ask what systems of known structure are most likely to provide information about hormone interactions. Here, I discussed enzyme-substrate, enzyme-(protein) inhibitor, enzyme fragment (S peptide), and antibody-hapten (or antigen) interactions as possible models. Following a study of a fairly inflexible hormone (insulin) and of a flexible hormone (glucagon), I commented on probable binding regions. Finally, my conclusion was that, at present, allosteric enzymes have many of the characteristics thought to be present in those hormone-receptor interactions which activate enzymes. This model does not necessarily apply in detail to examples of hormone interactions that affect permeability of the cell wall or activate genetic processes.