The oxygen-independent coproporphyrinogen III oxidase HemN utilizes harderoporphyrinogen as a reaction intermediate during conversion of coproporphyrinogen III to protoporphyrinogen IX

During heme biosynthesis the oxygen-independent coproporphyrinogen III oxidase HemN catalyzes the oxidative decarboxylation of the two propionate side chains on rings A and B of coproporphyrinogen III to the corresponding vinyl groups to yield protoporphyrinogen IX. Here, the sequence of the two decarboxylation steps during HemN catalysis was investigated. A reaction intermediate of HemN activity was isolated by HPLC analysis and identified as monovinyltripropionic acid porphyrin by mass spectrometry. This monovinylic reaction intermediate exhibited identical chromatographic behavior during HPLC analysis as harderoporphyrin (3-vinyl-8,13,17-tripropionic acid-2,7,12,18- tetramethylporphyrin). Furthermore, HemN was able to utilize chemically synthesized harderoporphyrinogen as substrate and converted it to protoporphyrinogen IX. These results suggest that during HemN catalysis the propionate side chain of ring A of coproporphyrinogen III is decarboxylated prior to that of ring B. © by Walter de Gruyter

Calix[4]arenes with 1,2- and 1,3-upper rim tetrathiafulvalene bridges

<div><p>Herein we report the synthesis of several calix[4]arene derivatives with tetrathiafulvalene bridges at the upper rim. Calix[4]arene-tetrathiafulvalene (TTF) conjugates <b>4a–d</b>, fixed in <i>cone</i> conformation and comprising two smaller 1,2-bridges, were prepared by cyclisation of tetrakis-chloromethylated calix[4]arene <b>1</b> with 2,3-dithiolates of TTFs. Larger calix[4]arene-TTF macrocycles <b>14</b> and <b>15</b>, also in <i>cone</i> conformation, contain 1,3-bridges and were synthesised by cyclisation of 2,6- and 2,7-dithiolates of TTFs with bis-bromomethylated calix[4]arene <b>7</b>. Redox properties of new calix[4]arene-TTF conjugates were characterised using cyclic voltammetry.</p></div

From icosahedron to a plane flattening dodecaiodo-dodecaborate by successive stripping of iodine

It has been shown by electrospray ionization–ion-trap mass spectrometry that B12I122− converts to an intact B12 cluster as a result of successive stripping of single iodine radicals or ions. Herein, the structure and stability of all intermediate B12In− species (n=11 to 1) determined by means of first-principles calculations are reported. The initial predominant loss of an iodine radical occurs most probably via the triplet state of B12I122−, and the reaction path for loss of an iodide ion from the singlet state crosses that from the triplet state. Experimentally, the boron clusters resulting from B12I122− through loss of either iodide or iodine occur at the same excitation energy in the ion trap. It is shown that the icosahedral B12 unit commonly observed in dodecaborate compounds is destabilized while losing iodine. The boron framework opens to nonicosahedral structures with five to seven iodine atoms left. The temperature of the ions has a considerable influence on the relative stability near the opening of the clusters. The most stable structures with five to seven iodine atoms are neither planar nor icosahedral.Spanish Ministerio de Ciencia e Innovación (CTQ2010–16237), CSIC (I3P grant to P.F.), the Generalitat de Catalunya (2009/SGR/00279), and the Center for Functional Nanomaterials (NanoFun) of Jacobs University Bremen.peer-reviewe

The Pseudomonas aeruginosa nirE gene encodes the S-adenosyl-L-methionine- dependent uroporphyrinogen III methyltransferase required for heme d1 biosynthesis

Biosynthesis of heme d1, the essential prosthetic group of the dissimilatory nitrite reductase cytochrome cd1, requires the methylation of the tetrapyrrole precursor uroporphyrinogen III at positions C-2 and C-7. We produced Pseudomonas aeruginosa NirE, a putative S-adenosyl-l-methionine (SAM)-dependent uroporphyrinogen III methyltransferase, as a recombinant protein in Escherichia coli and purified it to apparent homogeneity by metal chelate and gel filtration chromatography. Analytical gel filtration of purified NirE indicated that the recombinant protein is a homodimer. NirE was shown to be a SAM-dependent uroporphyrinogen III methyltransferase that catalyzes the conversion of uroporphyrinogen III into precorrin-2 in vivo and in vitro. A specific activity of 316.8 nmol of precorrin-2 h-1·mg-1 of NirE was found for the conversion of uroporphyrinogen III to precorrin-2. At high enzyme concentrations NirE catalyzed an overmethylation of uroporphyrinogen III, resulting in the formation of trimethylpyrrocorphin. Substrate inhibition was observed at uroporphyrinogen III concentrations above 17 m. The protein did bind SAM, although not with the same avidity as reported for other SAM-dependent uroporphyrinogen III methyltransferases involved in siroheme and cobalamin biosynthesis. A P. aeruginosa nirE transposon mutant was not complemented by native cobA encoding the SAM-dependent uroporphyrinogen III methyltransferase involved in cobalamin formation. However, bacterial growth of the nirE mutant was observed when cobA was constitutively expressed by a complementing plasmid, underscoring the special requirement of NirE for heme d1 biosynthesis