title: Thermal behavior and lipid composition of cauliflower plasma membranes in relation to ATPase activity and chilling sensitivity.
abstract: A plasma-membrane fraction rich in ion-stimulated ATPase activity was isolated from cauliflower (Brassica oleracea L.) buds. The activity of the ATPase was dependent on Mg(2+) and stimulated 4-fold by K(+). The lipids of the membrane fraction contained 57% by weight of phospholipid, 16% glycolipid including sterol glycosides, and 27% neutral lipids. Sterols and sterol esters comprised 9% by weight of the total lipid fraction, and the m ratio of total sterol to phospholipid was 0.5. Fatty acid unsaturation of the membrane lipids was 75%. Arrhenius plots of the Mg(2+) and Mg(2+) + K(+) stimulated ATPase activity were biphasic with an increase in activation energy occurring below about 12 degrees C, a response typical of some membrane-associated enzymes of chilling-sensitive plants. No thermal transitions were detected in the membranes or membrane lipids between 0 and 30 degrees C using differential scanning calorimetry and electron spin resonance spectroscopy. This type of thermal behavior is typical of membranes of chilling-resistant plants. It was concluded that the low temperature increase in activation energy of the ion-stimulated, membrane-associated ATPase is an intrinsic property of the enzyme system and not the result of a transition in the bulk membrane lipid.
authors: Plant Physiology Unit, Commonwealth Scientific and Industrial Research Organization, Division of Food Research and the School of Biological Sciences, Macquarie University, North Ryde, N.S.W., 2113, Australia.
authors: L C
authors: LC
authors: Wright
authors: E J
authors: EJ
authors: McMurchie
authors: M K
authors: MK
authors: Pomeroy
authors: J K
authors: JK
authors: Raison