Evidence has been presented indicating that the action of concentrated solutions of salts on bacterial respiration may be partly explained in terms of salting-out. It has been suggested that the material upon which this action is exerted is probably one of the proteins concerned in respiration, perhaps a dehydrogenating enzyme. This theory provides satisfactory explanations for: (
a
) the relation between salt concentration and rate of respiration or dehydrogenase activity; (
b
) the effect of temperature on this relation; and (
c
) the effect of pH on this relation, if it is further supposed that only the zwitterionic fraction of the protein is involved. The relative actions of various salts are in fair agreement with this suggestion, but provide no very convincing evidence either for or against it. The chief point of difficulty lies in the range of concentration over which the action is manifest. With halophilic bacteria, the evidence is consonant with the above view if the protein involved is one of high molecular weight. With normal organisms the salt concentrations are much lower than those causing salting-out. There is a little evidence that in normal organisms the dehydrogenating enzymes are less sensitive to salts than the intact cells, which may be the source of the discrepancy. No reason for this can yet be suggested, but the property must be absent from the enzymes of halophilic organisms, and whatever it is, its absence must be the foundation of the halophilic character.
A theory relating the action of salts on bacterial respiration to their influence on the solubility of proteins
