The influence of vitamin K-1 on the structure and phase behaviour of modelmembrane systems

Vitamin K-1 is a component of the Photosystem I of plants which constitutes the major dietary form of vitamin K. The major function of this vitamin is to be cofactor of the microsomal gamma-glutamylcarboxylase. Recently, nove l roles for this vitamin in the membrane have been postulated. To get insig ht into the influence of vitamin K-1 on the phospholipid component of the m embrane, we have studied the interaction between vitamin K-1 and model memb ranes composed of dimyristoylphosphatidylcholine (DMPC) and dielaidoylphosp hatidylethanolamine (DEPE). We utilized high-sensitivity differential scann ing calorimetry and small-angle X-ray diffraction techniques. Vitamin K-1 a ffected the thermotropic properties of the phospholipids, broadened and shi fted the transitions to lower temperatures, and produced the appearance of several peaks in the thermograms. The presence of the vitamin gave rise to the formation of vitamin-rich domains which were immiscible with the bulk p hospholipid in both the gel and the liquid-crystalline phases. Vitamin K-1 was unable to alter the lamellar organization of DMPC, but we found that it produced an increase in the interlamellar repeat spacing of DMPC at 10 deg rees C. Interestingly, vitamin K-1 promoted the formation of inverted hexag onal H-II structures in the DEPE system. We discuss the possible implicatio ns that these vitamin K-1-phospholipid interactions might have with respect to the biological function of the vitamin. (C) 1999 Elsevier Science B.V. All rights reserved.