Porphyrin level in normal, deficient, and transduced deficient LB cells. (A) LB cells were maintained in exponential phase of culture and then placed in culture at 2 × 10⁵cells/mL. After 48 hours, porphyrins were measured ([▧] Cell porphyrin level, [□] Supernatant porphyrin level) as described in Materials and Methods. Data are the mean ± SD of four to six determinations. ** P < .01 v noninfected LBN cells. (B) Porphyrin level in LBN cells, deficient LB45 cells, and a mixture (50/50) of LB45 and LBN cells. Cells were placed in culture at 2 × 10⁵ cells/mL. Porphyrin level was measured by spectrofluorimetry immediatly ([▨] 0 hour) and after 24 (□), 48 (▧), and 72 hours (▨), as described in Materials and Methods. Data are the means ± SD of six independent experiments.