(A-D) TMRE staining of human skin fibroblasts with a PEX19 mutation (Δ19T). Comparison of untreated and BSA-conjugated coconut oil–treated cells. Scale bars represent 10 μm. n = 10. (E) Concentration of free fatty acids in human skin fibroblast cell lysates in untreated and BSA-conjugated coconut oil–treated cells. In addition, Δ19T were cultured in the presence of BSA-conjugated coconut oil (+C), and samples were taken in the absence of coconut oil–BSA. n = 5. Error bars represent SD. * p < 0.05, ** p < 0.01. Significance tested using Student t test. Corresponding raw data can be found in supplemental file S1 Data. BSA, bovine serum albumine; NEFA, nonesterified fatty acid; PEX, peroxin; TMRE, tetramethylrhodamine ethyl ester.