J. Biol. Chem., Vol. 259, Issue 3, 1577-1585, 02, 1984
Proposed structure for the noncovalently associated heme prosthetic group of dissimilatory nitrite reductases. Identification of substituents
R Timkovich, MS Cork and PV Taylor
The substituents of the noncovalently associated heme prosthetic group of
the bacterial nitrite reductase-cytochrome oxidase (EC 1.9.6.1 or EC
1.9.3.2.) from Pseudomonas aeruginosa (ATCC 19429) and Paracoccus
denitrificans (ATCC 13456) have been identified. This was accomplished by
1H NMR, infrared, visible, and mass spectroscopic techniques applied to
semi-purified heme and purified methyl ester derivatives of the iron- free
porphyrin. The main structural features are as follows. 1) The macrocycle
is a reduced porphyrin of the chlorin type, that is, one of the pyrrole
rings has been saturated so that the beta-carbons have sp3- hybridization.
2) The chlorin is a tetracarboxylic acid. 3) The substituents of the
saturated pyrrole ring are two methyl groups and two hydroxymethyl groups.
4) The substituents of the unsaturated pyrrole rings are: (i) two methyl
groups (ii) a propionic acid (iii) an acrylic acid, and (iv) two directly
bonded formic acid groups. No firm evidence has been obtained for the
relative positions of these unsaturated beta-pyrrolic substituents around
the macrocyclic ring, but a proposed structure will be discussed. Several
previously inexplicable chemical properties of the heme in extracts or in
the intact enzyme can be now interpreted in view of the proposed structure.
The trivial name "acrylochlorin" is suggested for the macrocycle.
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