addition reaction or addition any organic chemical reaction involving the combination of two or more substances to form a single product in which there are more groups attached to carbon atoms than there were in the original reactants. Such reactions thus involve a net reduction of bond multiplicity in one of the reactants, as in
active-enzyme centrifugation a technique for determining the sedimentation and diffusion coefficients of an enzyme– substrate complex. A thin lamella of an enzyme solution is layered onto a substrate solution in an ultracentrifuge cell and, on rotation, as the enzyme molecules sediment in a band through the substrate solution they catalyse the enzymic reaction, the progress
activation 1 the action or process of rendering an atom, molecule, or other substance reactive or more reactive, whether physicochemically, chemically, or biochemically. 2 the process of rendering material artificially radioactive: radioactivation. See radioactivation analysis. 3 the initial changes in an ovum during fertilization, covering the periodfrom first contact with a sperm to dissolution of