KINETICS OF ENZYMATIC PHOTOREACTIVATION STUDIED WITH PHAGE T1 AND ESCHERZCHZA COLI Bs‐1*

Abstract

Abstract— The kinetics of enzymatic photoreactivation (PR) of u.v.‐induced killing was compared among E. coli Bs‐1, phage T1 in Bs‐1 and phage T1 in irradiated Bs‐1. The PR action spectrum showed no substantial difference between PR of Bs‐1 and PR of T1 in Bs‐1. The PR D37 (i.e. the PR dose required to reactivate all but 37 per cent of the reactivable lethal lesions) was found to decrease linearly with decreasing U.V. dose whether U.V. was given to produce pyrimidine dimers in Bs‐1 DNA, which then compete with irradiated T1 DNA for PR enzyme, or to Bs‐1 or T1 DNA to produce dimers serving as substrate for the PR enzyme. A generalized Michaelis‐Menten formula was used to analyze the data and the following conclusions were drawn. (1) The number of PR enzyme molecules per cell available for PR of T1 DNA inside the Bs‐1 host is only a quarter of the number available for PR of the Bs‐1 host itself. (2) The Michaelis constant Km for reaction of host‐DNA‐damage and PR‐enzyme becomes larger when the host damage acts as competitive inhibitor to PR of T1 DNA than when it is the substrate for PR enzyme. (3) PR enzyme retains almost all its initial catalytic efficiency even after about two‐hundred rounds of catalytic functioning. Conclusions (1) and (2) suggest that PR enzyme is concentrated within the nuclear area surrounding the host DNA.