ALLOMETRY OF MITOCHONDRIAL PROTON LEAK - INFLUENCE OF MEMBRANE-SURFACE AREA AND FATTY-ACID COMPOSITION

We investigated why liver mitochondria from small mammals are leakier to protons than those from larger mammals. Sixty-nine percent (+/-23%) of the proton leak differences appeared to relate to membrane area (l ess inner membrane surface area in larger animals); any residual diffe rences must reflect differences in membrane properties. There were dif ferences in phospholipid fatty acid composition; unsaturation index, m onounsaturates, palmitate (16:0), stearate (18:0), docosahexaenoate [2 2:6(n-3)], and the 22:6(n-3) ratio all correlated with body mass. Prot on flux per square centimeter did not correlate significantly with bod y mass or, in general, with phospholipid fatty acid composition, sugge sting little role for fatty acid composition in determining proton lea k in mammals of different body mass. However, unsaturation index and n -3 polyunsaturated fatty acid content correlated significantly with pr oton leak per milligram phospholipid when literature data from reptile s and rats in different thyroid states were included, giving some supp ort to suggestions of a general role for phospholipid fatty acid compo sition in determining mitochondrial proton leak.