Open AccessRadiation inactivation of oligomeric enzyme systems: theoretical considerations.
Author(s) -
A. S. Verkman,
Karl Skorecki,
Dennis A. Ausiello
Publication year - 1984
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.81.1.150
Subject(s) - oligomer , monomer , enzyme , chemistry , exponential function , yield (engineering) , function (biology) , exponential growth , radiation , biophysics , biochemistry , thermodynamics , biology , organic chemistry , physics , polymer , mathematics , optics , quantum mechanics , mathematical analysis , evolutionary biology
Radiation inactivation has been used as a tool to explore the size, structure, and function of soluble and membrane-bound enzymes. Enzyme systems consisting of a single functional unit yield a single exponential dependence of enzyme activity on radiation dose. Complex, nonexponential, inactivation curves suggest the presence of a multiunit enzyme system. A concave-upward inactivation curve suggests the presence of multiple independent functional units of distinct size and activity that do not interact with each other. An oligomeric enzyme, consisting of n identical subunits in equilibrium with monomers, can give simple exponential decay curves or more complex inactivation curves with various degrees of upward or downward concavity, depending upon the extent of oligomer-monomer equilibration among subunits after radiation, oligomer-to-monomer size and activity ratios, and multihit requirements for oligomer inactivation. For each of these possibilities, equations for the inactivation curves are derived, calculated numerically, and discussed in qualitative terms. A systematic approach to the evaluation of complex radiation inactivation curves is proposed and limitations of the radiation inactivation method are reviewed.