The V¹⁹⁰ mutant can function in mitochondria. Wild type and mutant ALAS-E proteins were expressed in QT6 cells. Panel A shows cell homogenate under normal lamp. The porphyrin accumulation in the cells was measured by exposing the cell homogenate (B) and culture supernatant (C) to UV light. Tube 1 contains cells transfected with control plasmid. Cell homogenate and culture supernatant expressing wild type ALAS-E (tube 2) displays an intense red fluorescence under UV lamp, indicating the presence of porphyrins. Expression of the V¹⁹⁰ mutant (tube 3) also gave rise to red fluorescence, albeit of weaker intensity than wild type, while cell homogenate and culture supernatant transfected with the V⁴²⁶ mutant plasmid (tube 4) showed only marginal red fluorescence.