Since ALAS catalyzes the rate-determining step of tetrapyrrole biosynthesis in mammals, overexpression of ALAS in prokaryotic and eukaryotic cells Choline Chloride results in accumulation of the photosensitizing heme precursor, protoporphyrin IX. This property has potential for applications of ALAS or ALAS variants in photodynamic therapy of tumors and other nonmalignant dermatological indications, such as acne vulgaris, psoriasis, and scleroderma. In this study, we transfected mammalian cells with MaLAS2 variants and measured PPIX accumulation using fluorescence activated cell sorting. We identified the R433K variant with additional mutations of the HRMs in the presequence as the variant causing the most cellular PPIX accumulation. Subsequently, we used the variants causing the most PPIX accumulation to study the cell death caused by the PPIX toxicity and photosensitization. Deferoxamine is a well-characterized iron-specific bacterial siderophore with a long Pamidronate disodium history of clinical use in iron chelation therapy. Deferoxamine has the potential to increase PPIX by decreasing the cellular iron concentration, thereby inhibiting the conversion of PPIX to heme. Treatment of K562 cells with deferoxamine for 18 hours caused no change in PPIX fluorescence in cells not expressing mALAS2 or cells expressing HPVT. Deferoxamine did cause a significant increase in PPIX in cells expressing WT, in which case the mean PPIX fluorescence increased from 1.4-fold over cells expressing ZsGreen1, to 2.4-fold with deferoxamine. To evaluate cellular intactness and accumulated PPIX distribution in the transfected HeLa cells, we used confocal microscopy to visualize the fluorescent PPIX in individual HeLa cells and HeLa cells transfected with either the pIRES2ZsGreen1 vector or pEF31. Transfected cells were grown in medium supplemented with 100 mM glycine for 18 hours in preparation for imaging. The outline of intact cells, and thus their morphological integrity, was evident in the three cases. As expected, green fluorescence was visualized in the transfected but not control HeLa cells. In fact, green fluorescence, arising from the soluble ZsGreen1 green fluorescent protein was observed evenly distributed throughout the cytoplasm of the HeLa cells transfected with either pIRES2 ZsGreen1 or the R433K-expression plasmid.