Formation of Zinc Protoporphyrin IX form Myoglobin with Pork Loin Extract

Ferrochelatase Catalyzes the Formation of Zn-protoporphyrin of Dry-Cured Ham via the Conversion Reaction from Heme in Meat

“…First, an intermediate porphyrin, protoporphyrinogen, is oxidized by protoporphyrinogen oxidase to form protoporphyrin aerobically; then, Zn-protoporphyrin is produced by the insertion of zinc, which is present in large amounts in meat, into the protoporphyrin . The other pathway, also identified in our findings, is that Zn-protoporphyrin is generated via the conversion reaction of heme, in which zinc is inserted into protoporphyrin as a product of the iron-removal reaction of heme in hemoproteins catalyzed by FECH. ,, In this case, the replacement does not occur easily, especially in porcine muscle (meat). FECH from porcine muscle mitochondria catalyzes the insertion reaction of zinc into protoporphyrin to form Zn-protoporphyrin ,, as well as the iron-removal reaction of heme, strongly suggesting that FECH acts as a conversion enzyme in porcine meat.…”

“…The present study first demonstrated that highly efficient iron removal and subsequent conversion of heme in meat to Zn-protoporphyrin occur upon a relatively short period of incubation, via the catalysis of FECH. The replacement of iron by zinc in the formation of Zn-protoporphyrin was noted previously. − Our previous studies , showed that the formation of Zn-protoporphyrin can take place via the reverse and conversion reactions and was catalyzed by FECH. However, the level of production of Zn-protoporphyrin from heme is low because the reaction of FECH precisely proceeds to the metal ion-insertion (forward) reaction.…”

“…It was reported that meat extracts acted as the enzyme sources for Zn-protoporphyrin formation, ,, and the iron-removal and conversion reactions of myoglobin to Zn-protoporphyrin were successfully demonstrated. − Although exogenous protoporphyrin, myoglobin, and zinc ions were added as substrates for these reaction mixtures, the yield in the formation was low. The present data showed that not only porcine FECH in porcine muscle (raw meat) but also yeast FECH as exogenously added enzyme used the endogenous myoglobin-heme in meat as a substrate, promoting the iron-removal and conversion reactions of heme to Zn-protoporphyrin.…”

“…Several findings showed that bacteria in porcine meat were the main cause of the stable pigments during Parma ham processing . Recently, endogenous enzymes including FECH in meat have been identified as a potential cause of the pigment formation. − Several compounds such as salt, ascorbic acid, and dithiothreitol can increase the formation of Zn-protoporphyrin to some extent. − It is possible that the formation of Zn-protoporphyrin could occur via two pathways. First, an intermediate porphyrin, protoporphyrinogen, is oxidized by protoporphyrinogen oxidase to form protoporphyrin aerobically; then, Zn-protoporphyrin is produced by the insertion of zinc, which is present in large amounts in meat, into the protoporphyrin .…”