Refsum disease diagnostic marker phytanic acid alters the physical state of membrane proteins of liver mitochondria

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid), a branched chain fa tty acid accumulating in Refsum disease to high levels throughout the body, induces uncoupling of rat liver mitochondria similar to non-branched fatty acids (e.g. palmitic acid), but the contribution of the ADP/ATP carrier or the aspartate/glutamate carrier in phytanic acid-induced uncoupling is of minor importance. Possible deleterious effects of phytanic acid on membrane -linked energy coupling processes were studied by ESR spectroscopy using ra t liver mitochondria and a membrane preparation labeled with the lipid-spec ific spin probe 5-doxylstearic acid (5-DSA) or the protein-specific spin pr obe MAL-TEMPO (4-maleimido-2,2,6,6-tetramethyl-piperidine-1-oxyl), The effe cts of phytanic acid on phospholipid molecular dynamics and on the physical state of membrane proteins were quantified by estimation of the order para meter or the ratio of the amplitudes of the weakly to strongly immobilized MAL-TEMPO binding sites (W/S ratio), respectively. It was found, that phyta nic acid (1) increased the mobility of phospholipid molecules (indicated by a decrease in the order parameter) and (2) altered the conformational stat e and/or the segmental mobility of membrane proteins (indicated by a drasti c decrease in the W/S ratio). Unsaturated fatty acids with multiple cis-dou ble bonds (e.g. linolenic or arachidonic acid), but not nonbranched FFA (ra nging from chain length C10:0 to C18:0), also decrease the W/S ratio. It is hypothesized that the interaction of phytanic acid with transmembrane prot eins might stimulate the proton permeability through the mitochondrial inne r membrane according to a mechanism, different to a protein-supported fatty acid cycling. (C) 1999 Federation of European Biochemical Societies.