The formation of zinc protoporphyrin IX (ZPP) in porcine heart extract was investigated by visible absorption and fluorescent spectral analysis. Characteristic absorption peaks of ZPP were observed at .+1, /.0, and /2. nm after anaerobic incubation of the extract with metmyoglobin and ZnCl, in the dark at -*ῌ for 1, h. In the fluorescent spectra (excitation : .+* nm), a strong peak due to ZPP was obtained at /23 nm. The time-course study showed that ZPP formation greatly increased after a lag period, during which metmyoglobin was reduced. ZPP formation was significantly facilitated by the use of oxymyoglobin. Zinc chelatase activity in the extract was estimated as +-2 mU/mL-extract and its specific activity was ,.3/ mU/mg-protein. The di#erence in activities with aerobic and anaerobic incubation was not significant. Measurements at pH /./ῌ1.* showed that activities were higher at lower pH. The activity of zinc chelatase was stimulated by the presence of ATP, and the highest activity was obtained at an ATP concentration of ,./ mg/mL.
The formation of zinc protoporphyrin IX (ZnPP) and protoporphyrin IX (PP) in porcine heart mitochondria was investigated by fluorescent spectral analysis. The time-course study at -1῍C and pH /./ with +** mM ZnCl, showed a linear formation of ZnPP from oxymyoglobin after a lag-period (3 h) at the formation rate of *..0 nmol/h. The formed amount of ZnPP is dependent upon the ZnCl, concentration. In the incubation without ZnCl,, the new peak derived from PP appeared at 0--nm after +, h, and then its intensity gradually increased. The formation of PP is believed to be due to the release of Fe ,ῌ in porphyrin ring of oxymyoglobin during the incubation. This suggests that the mitochondria have the ability to form PP from oxymyoglobin, and therefore, are directly related to the release of Fe ,ῌ from porphyrin ring in myoglobin.
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