Abstract
Target size analysis of radiation inactivation has been used to determine structural features of hormone receptors and adenylate cyclase. This method allows the determination of molecular sizes of components of enzyme- or receptor-systems in impure preparations and in intact membranes. Principles of application of target size analysis and basic concepts for interpretation are discussed. Reviewing both biochemical and target size data on insulin receptors and adenylate cyclase it is attempted to outline the potential and the limitations of this biophysical approach.