THE NATURE OF THE CYTOTOXIC ACTION OF UNDISSOCIATED IODOACETIC ACID IN YEAST CELLS

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Abstract
In order to determine the mechanism of the inhibition produced by undis sociated iodoacetic acid, intact cells of baker’s yeast were exposed to a 1.5 × 10−3 M solution of the inhibitor at pH 4.5. After washing and drying the cells, various enzyme solutions were prepared from them and their activities determined. Zymase, carboxylase, and catalase, as well as lactic and alcohol dehydrogenases were almost totally inactivated by exposure to the inhibitor. Evidence, at least with respect to zymase, indicates that the inhibition arises as a result of an inactivation of the protein components of the system. Thus the mechanism of action of undissociated iodoacetic acid appears to differ in several respects from that characteristic of the iodoacetyl ion whereas the ionic form of the acid produces an inhibition which is freely reversible and is more specifically associated with an inactivation of sulphohydryl groups, the inhibition resulting from the action of the molecular species is irreversible and nonspecific in nature.

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