both enzymatic activities are measured by recording protoporphyrin ix fluorescence increase in air-saturated buffer in the presence of edta ( to inhibit ferrochelatase that can further metabolize protoporphyrin ix ) and in the presence of dithiothreitol ( that prevents nonenzymatic oxidation of porphyrinogens to porphyrins ) .
C0033733
protoporphyrin ix
C0032712
porphyrins