Inhibition of protohaem ferro-lyase by N-substituted porphyrins. Structural requirements for the inhibitory effect

Abstract

N-Methyl mesoporphyrin was a powerful inhibitor of protohaem ferro-lyase in vitro, whereas N-ethyl mesoporphyrin and N-methyl coproporphyrin were not and neither was the newly described green pigment produced by giving rats ethylene. This suggests that the size of the substituent at a pyrrole nitrogen and also the number of carboxylic acid side chains of the substituted porphyrin are important for the inhibitory effect. Evidence that N-methyl mesoporphyrin inhibited the enzyme, whereas the ethylene-derived pigment did not, was also obtained in vivo.

Structural Isomerism and chirality of N‐monosubstituted protoporphyrins

“…Male mice were treated with DDC and phenobarbitone-pretreated male rats were exposed to ethylene or given a single injection of 2-allyl-24sopropylacet-amide or of secobarbitone [5-allyl-5(1-methylbutyl)-barbiturate], as in [5,6]. The corresponding N-substituted porphyrins or green pigments were extracted from liver homogenates, chromatographed on Sephadex LH-20 [5] and further purified by TLC [6] after methylation of the propionate sideehains by reaction with BF 3 in methanol [8].…”

“…The corresponding N-substituted porphyrins or green pigments were extracted from liver homogenates, chromatographed on Sephadex LH-20 [5] and further purified by TLC [6] after methylation of the propionate sideehains by reaction with BF 3 in methanol [8].…”

“…Interaction of the inhibitory porphyrin with the active centre of ferrochelatase is important for inhibition of the enzyme [5,6]. Authentic N-methylated meso and protoporphyrin have been synthesized and shown to be powerful inhibitors of the enzyme in vivo and in vitro [2,6,7]. Synthetic N-methyl protoporphyrin could be separated by high-performance liquid chromatography (HPLC) into 2 separate fractions possessing different inhibitory activity and possibly representing different structural isomers, where different pyrrole nitrogens had been methylated [2].…”

“…Interaction of the inhibitory porphyrin with the active centre of ferrochelatase is important for inhibition of the enzyme [5,6]. Authentic N-methylated meso and protoporphyrin have been synthesized and shown to be powerful inhibitors of the enzyme in vivo and in vitro [2,6,7].…”

Substrate interactions with human ferrochelatase

“…Since the initial work by DeMatteis' group that identified and characterized the ''green pigment'' in livers of 3,5-dicarbethoxy-1,4-dihydrocollidine-treated mice as N-methylprotoporphyrin, there has been considerable interest in N-alkylporphyrins as inhibitors of ferrochelatase (9)(10)(11)(12). Because of the tight binding competitive inhibition of ferrochelatase by N-methylprotoporphyrin (13), the fact that nonenzymatic metal insertion into porphyrins is facilitated by macrocycle distortion, and the observation that an antibody raised against N-methylmesoporphyrin (N-MeMP) IX catalyzes the insertion of metal ions (14)(15)(16)(17), the general hypothesis has been that N-alkyl porphyrins are transition-state analogs (18)(19)(20).…”