[Role of lipids in the function of microsomal electron transport chains of potato].

Microsomal membranes from potato tubers were extracted by acetone solutions of increasing concentrations (5, 10, 15, 20, 30, 40, 50, 70 and 90 p. cent). Microsomal lipids were progressively extracted: acetone concentrations exceeding 30 p. cent extracted large amounts of membraneous phospholipids (figure). Lipid extraction reduced NADH-cytochrome c reductase activity but did not affect NADH-ferricyanide reductase and NADPH-cytochrome c reductase activities. This was confirmed by experiments using increasing concentrations of sodium deoxycholate. After lipid extraction with acetone (or solubilization by triton X100), NADH-cytochrome c reductase activity of microsomal membranes could not be recovered by adding back lipids under various experimental conditions. These results strongly suggest that, in potato microsomes, lipids are undispensable components of the electron transport chain starting from NADH especially in the portion involving cytochrome b5. On the contrary, the second microsomal electron transport chain, starting from NADPH, is not regulated by lipids. However, plant microsomal membranes would be much more disturbed by liped extraction than animal microsomes and suitable relipidation conditions remain to be found to prove definitely the lipid dependence of plant microsomal electron transport.