Bacterial luciferase catalyzes the remarkable conversion of chemical energy in the form of reduced flavin mononucleotide (FMNH2), a long chain aliphatic aldehyde (RCHO), and oxygen into chemical products, heat, and light according to the reaction: FMNH2 plus RCHO plus O2 yields sub E FMN plus RCOO ion plus H3O ion plus h nu. Our recent calorimetric studies have demonstrated that this reaction occurs with a total enthalpy change of Ql equals minus 81.3 kcal (mole FMN) at 25 degrees C and pH 7.0. To aid in the interpretation of this heat effect and other data we have obtained, a new parameter has been defined, QI, the intrinsic heat of the chemiluminescent reaction: QI equals QL minus h nu. This proposal outlines studies designed to further our understanding of bioluminescence using this parameter. It obviously is useful in separating thermal effects due to light emission from the total thermochemistry of the reaction. Thus, it is useful in comparing the thermochemistry of any chemiluminescent process, e.g. from model compounds (dioxetanes), bacteria or fireflies. Bacterial luciferase is an (alpha beta) dimer. The enzymatic activity is definitely coupled to the quaternary structure. Ultracentrifugal studies and enzymatic studies have demonstrated the reversible reaction alpha plus beta reversibly yields (alpha beta). This proposal outlines our further studies of this quaternary structure and demonstrates the utility of the mutants in understanding the type bonds acting to stabilize the dimer. These studies are designed to increase our understanding of bioluminescence at a molecular level using a chemical and thermodynamic approach. The knowledge we gain from these studies will be important in our development of a thermodynamic description of enzyme activity and quaternary structure.