[Functional and structural changes of E. coli membranes induced by low temperature freezing].

Low temperature freezing of E. coli cells causes a fall in endogenous respiration and stimulation of respiration by the non-penetrant substrate NADH. This decrease is not due to disturbances in the function of electron transport chain, since the dehydrogenase and oxidase activities and cytochrome content in the membranes of intact and frozen cells are practically the same. Frozen E. coli cells are incapable of ATP synthesis by artificial proton motive force, although the ATPase activity of isolated membranes is not changed. The disturbances in the penetrability barrier of protons after freezing can be revealed from changes in pH of cell suspensions after rapid acidification. It is assumed that the cell penetrability barrier undergoes alterations causing a loss of respiration substrates and, probably, oxidative phosphorylation uncoupling. A correlation between constant damages of the membrane penetrability barrier and cell survival was established. Using spin labelling of different localization, the changes in the state of membrane surface at the intact hydrophobic lipid zone were demonstrated. It was found that freezing does not induce lipid peroxidation.