J. Biol. Chem., Vol. 259, Issue 24, 15089-15093, Dec, 1984
Proposed structure for the noncovalently associated heme prosthetic group of dissimilatory nitrite reductases. Configuration of substituents of acrylochlorin
R Timkovich, MS Cork and PV Taylor
The configuration of the substituents around the macrocycle core has been
determined for acrylochlorin, the reduced porphyrin that is the iron-free
form of heme d1. This has been accomplished by two independent techniques.
Nuclear Overhauser enhancements on the proton resonances of acrylochlorin
d3-methyl ester were measured to determine nearest-neighbor substituents
and mesoprotons. A lanthanide shift reagent,
tris-(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-di onato)
europium(III), was found to bind in the vicinity of the carbonyl oxygens of
the propionate and acrylate methyl esters. Differential chemical shift
effects on the proton resonances of acrylochlorin provided evidence on
relative distances from the lanthanide-binding site. Since the substituents
are constrained along the circumference of the macrocycle, this provided
information on configuration. Assuming that the dominant mechanism for
spin-lattice relaxation in acrylochlorin in deuterated chloroform solution
is proton dipole-dipole interaction, measured values of spin-lattice
relaxation times could be interpreted as being consistent with the proposed
configuration. The configuration bears sufficient similarity to that of
protoporphyrin IX so that a common nomenclature may be used (Smith K. M.
(ed) (1975) Porphyrins and Metalloporphyrins, pp. 3-5,
Elsevier/North-Holland Biomedical Press, Amsterdam). The deduced
configuration of the acrylochlorin methyl ester is: 1-methyl,
1-hydroxymethyl, 2-methyl, 2- hydroxymethyl, 3-methyl formate, 4-methyl
formate, 5-methyl, 6-methyl propionate, 7-methyl acrylate, 8-methyl. The
naturally occurring heme d1 has free carboxylic acids at the 3-, 4-, 6-,
and 7-positions.
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