Mutants of Escherichia coli K12 permeable to haemin

Mutants of Escherichia coli which require 5-aminolaevulinic acid (5-ALA), the first intermediate of haem biosynthesis, do not respond to haemin and porphyrins. The probable explanation of the lack of response is that E. coli may be impermeable to haemin and porphyrins. Mutants are described which responded to haemin and porphyrins as well as to 5-ALA. Indirect evidence is presented that the mutants were permeable to haemin. The mutants showed other phenotypic changes, and resembled some mutants which are known to have changes in the cell envelope.