Abstract
An investigation of the kinetics of photoreactivation (PR) in stationary phase cells of the UV-sensitive Escherichia coli mutant K12 AB2480 revealed an initial fast rate of PR which can be attributed to the photolysis of photoreactivating enzyme-substrate complexes already in existence at the start of the illumination period. The initial fast rate could be eliminated by administering a single high intensity flash at the start of continuous illumination. This experimental technique allowed the recognition of 2 additional rate processes during continuous illumination. The first order rate constant for the faster rate process ( kf) leads to a value of 4–5 photoreactivating enzyme (PRE) molecules per cell for 16 h nutrient broth grown cells. A photoreactivating irradiance of approx. 60 erg mm −2 sec −1 saturates the reaction and under saturating conditions we obtain a value for the activation energy of the fast rate of 9 kcal mole −1.
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