Protection From Visible Light Damage to Enzymes and Transport in Escherichia Coli*

Cysteine, anthranilic acid and adenine, in decreasing order of effectiveness, protected flavo‐enzymes of E. coli against inactivation with high‐intensity, heterochromatic light above 400 nm. Cell suspensions illuminated for 40 min in the presence of cysteine retained 30, 40 and 55% of their succinate, l ‐α‐glycerophosphate and d ‐lactate dehydrogenase activities, whereas less than 10% activity could be detected in the absence of this protective agent. Different effects on respiration and transport systems were obtained with these protective agents. Adenine and anthranilic acid provided substantial protection of the glycine and methylthio‐ß‐ d ‐galactoside transport systems but failed to attenuate adverse light effects on respiration and phenylalanine uptake. Cysteine did not protect respiration and potentiated damage to selected transport systems. Our results suggest that flavins act as photosensitizers.