Biosynthesis of hemed1, the essential prosthetic group of the dissimilatory nitrite reductase cytochromecd1 , requires the methylation of the tetrapyr-role precursor uroporphyrinogen III at positions C-2 and C-7. We pro-duced Pseudomonas aeruginosaNirE, a putativeS-adenosyl-l-methionine (SAM)-dependent uroporphyrinogen III methyltransferase, as a recombi-nant protein inEscherichia coliand purified it to apparent homogeneity by metal chelate and gel filtration chromatography.
