NON-IRON PORPHYRINS CAUSE TUMBLING TO BLUE-LIGHT BY AN ESCHERICHIA-COLI MUTANT DEFECTIVE IN HEMG

Previously we showed that an Escherichia coil hemH mutant, defective i n the ultimate step of heme synthesis, ferrochelatase, is somewhat bet ter than 100-fold more sensitive than its wild-type parent in tumbling to blue light, Here we explore the effect of a hemG mutant, defective in the penultimate step, protoporphyrinogen oxidase. We found that a hemG mutant also is somewhat better than 100-fold more sensitive in tu mbling to blue light compared to its wild-type parent. The amount of n on-iron porphyrins accumulated in hemG or hemH mutants was more than 1 00-fold greater than in wild type. The nature of these accumulated por phyrins is described. When heme was present, as in the wild type, the non-iron (non-heme) porphyrins were maintained at a relatively low con centration and tumbling to blue light at an intensity effective for he mG or kemH did not occur. The function of tumbling to light is most li kely to allow escape from the lethality of intense light.