Phospholipids and polypeptides in the outer membrane of maize mitochondria

The outer membrane from mitochondria of etiolated maize epicotyls was isolated by a shrinkage-swelling-shrinkage procedure. The polypeptide pattern of the outer membrane revealed five porin isoforms (M(r)s 33 000-34 000) in the pi region between 6.7 and 7.5. The phospholipid composition of the outer membrane was characterized by avery high phosphatidylcholine/phosphatidylethanolamine ratio, a significant amount of phosphatidylinositol and a low double bond index value. Analysis of molecular species by HPLC showed that 16:0/18:2 molecules of phosphatidylcholine and phosphatidylethanolamine were more specifically associated with the outer membrane, while 18:2/18:2 molecules were preferentially localized in the inner membrane. The results are discussed in relation to the biogenesis of mitochondrial lipids. Copyright (C) 1996 Published by Elsevier Science Ltd