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Abstract The regulation of an urgent stress adaptive mechanism of Pseudomonas putida, the isomerization of cis‐ to trans‐unsaturated fatty acids, was investigated. By comparing the responses of the cells to a series of stress factors, a direct correlation between the activation of this unique mechanism and the well‐investigated K+‐uptake pumps was observed. Only those stress conditions (osmotic stress caused by glycerol, cold shock, high pH) that are well known not to activate cellular K+‐uptake, showed no effect on the cis‐trans isomerase (cti). On the other hand, organic solvents, osmotic stress caused by NaCl and sucrose, heavy metals, heat shock and membrane‐active antibiotics activated both K+‐uptake and the cti system. This seems to be another indication for an activation of the constitutively present cti by increasing membrane fluidity. The enzyme, which is located in the periplasma, can only reach its substrate, the double bond in the hydrophobic zone of the membrane bilayer, when the membrane fluidity is disturbed by an environmental factor.
Neumann et al. (Mon,) studied this question.