A 2-STEP REVERSIBLE-IRREVERSIBLE MODEL CAN ACCOUNT FOR A NEGATIVE ACTIVATION-ENERGY IN AN ARRHENIUS PLOT

Arrhenius plots of the rate of inactivation (killing) of mammalian cel ls and Drosophila embryos have ''apparent negative'' activation energi es at low temperatures. This can be explained by assuming that the rat e-limiting event resulting in killing is a two-step process or mechani sm, where the first step is reversible and the second irreversible. Tw o examples, consistent with this model, are suggested as possible mech anisms of hypothermic killing: (i) a membrane lipid liquid crystalline -to-gel transition followed by a metabolic block or event which kills the cell and (ii) cold denaturation of a protein followed by protein a ggregation. (C) 1996 Academic Press, Inc.