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First published online September 14, 2007
Journal of Experimental Biology 210, 3440-3450 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.007286

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Differences in membrane acyl phospholipid composition between an endothermic mammal and an ectothermic reptile are not limited to any phospholipid class

Todd W. Mitchell^1,2, Kim Ekroos³, Stephen J. Blanksby⁴, Anthony J. Hulbert^1,5 and Paul L. Else^1,2,*

¹ Metabolic Research Centre, University of Wollongong, NSW, 2522, Australia
² School of Health Sciences, University of Wollongong, NSW, 2522, Australia
³ AstraZeneca R&D, 41383 Mölndal, Sweden
⁴ Department of Chemistry, University of Wollongong, NSW, 2522, Australia
⁵ School of Biological Sciences, University of Wollongong, NSW, 2522, Australia

^* Author for correspondence (e-mail: pelse{at}uow.edu.au)

Accepted 24 July 2007

This study examined questions concerning differences in the acyl composition of membrane phospholipids that have been linked to the faster rates of metabolic processes in endotherms versus ectotherms. In liver, kidney, heart and brain of the ectothermic reptile, Trachydosaurus rugosus, and the endothermic mammal, Rattus norvegicus, previous findings of fewer unsaturates but a greater unsaturation index (UI) in membranes of the mammal versus those of the reptile were confirmed. Moreover, the study showed that the distribution of phospholipid head-group classes was similar in the same tissues of the reptile and mammal and that the differences in acyl composition were present in all phospholipid classes analysed, suggesting a role for the physical over the chemical properties of membranes in determining the faster rates of metabolic processes in endotherms. The most common phosphatidylcholine (PC) molecules present in all tissues (except brain) of the reptile were 16:0/18:1, 16:0/18:2, 18:0/18:2, 18:1/18:1 and 18:1/18:2, whereas arachidonic acid (20:4), containing PCs 16:0/20:4, 18:0/20:4, were the common molecules in the mammal. The most abundant phosphatidylethanolamines (PE) used in the tissue of the reptile were 18:0/18:2, 18:0/20:4, 18:1/18:1, 18:1/18:2 and 18:1/20:4, compared to 16:0/18:2, 16:0/20:4, 16:0/22:6, 18:0/20:4, 18:0/22:6 and 18:1/20:4 in the mammal. UI differences were primarily due to arachidonic acid found in both PC and PEs, whereas docosahexaenoic acid (22:6) was a lesser contributor mainly within PEs and essentially absent in the kidney. The phospholipid composition of brain was more similar in the reptile and mammal compared to those of other tissues.

Key words: fatty acid, metabolism, lipid, mass spectrometry, glycerophospholipid, reptile, mammal, endothermy, ectothermy

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