The compound mutant Dnf1N220S,L1202P increases the specificity of SM transport. (A and B) A time course of NBD-PC (A) and NBD-SM (B) uptake in Dnf1WT, Dnf1N220S, and Dnf1N220S,L1202P. Time points were taken at 0 min (n = 9), 15 min (n = 9), 25 min (n = 3), 27 min (n = 3), 30 min (n = 3), and 60 min (n = 9) ± SEM. Error bars indicate SEM. (C) A table presenting the slope of the linear regression fits in A and B, demonstrating that Dnf1N220S and Dnf1N220S,L1202P have reduced rates of NBD-PC uptake and increased rates of NBD-SM uptake relative to Dnf1WT.