Technique for quantification of erythrocyte zinc protoporphyrin IX and protoporphyrin IX
In heme biosynthesis, the terminal step is the insertion of ferrous iron into protoporphyrin IX (PPIX) by the enzyme ferrochelatase. Under physiological conditions, small amounts of zinc protoporphyrin IX (ZnPP) are formed as well. The concentrations of ZnPP and PPIX in erythroid cells are characteristically altered by conditions that affect the availability of ferrous iron, increase the amounts of PPIX, or diminish the enzymatic activity of ferrochelatase. Unfortunately, the standard HPLC-based quantification method is time-consuming and complicated. Alternatives, too, have proven too technically demanding or cumbersome for general adoption. For measurement of ZnPP alone, a portable front-face fluorometer, the hematofluorometer, is commercially available. Yet, its use is limited by a high background fluorescence of other blood constituents making sample washing inevitable.