1. The ability of homologous series of alcohols, ketones, and aldehydes to cause alteration of intracellular catalase increases approximately threefold for each methylene group added, thus following Traube's rule. Equiactive concentrations of alcohols (methanol to octanol) varied over a 4,000-fold range, yet the average corresponding surface tension was 42 ± 2 dynes/cm., that for ketones 43 ± 2, and for aldehydes (above C1) 41 ± 3.

2. Above C8 the altering activity of alcohols ceased to follow Traube's rule, and at C18 was nil. Yet the surface activities of alcohols from nonanol to dodecanol did follow Traube's rule. These two facts show that the interface which is being affected by these agents is not the cell surface, for if it were, altering activity should not fall off between C9 and C12 where surface activity is undiminished; they show also that micelle formation by short range association of hydrocarbon "tails," usually invoked to explain decrease in biological activity of compounds above C8, is not responsible for this effect in these experiments, in which permeability of the cell membrane probably is involved.

3. The most soluble alcohols and aldehydes (alcohols C1 to C8; aldehydes C1, C2), but not ketones, cause, above optimal concentration, an irreversible inhibition of yeast catalase.

4. The critical concentration of altering agent (i.e., that concentration just sufficient to cause doubling of the catalase activity of the yeast suspension) was independent of the concentration of the yeast cells.

5. Viability studies show that the number of yeast cells killed by the altering agents was not related to the degree of activation of the catalase produced. While all the cells were invariably killed by concentrations of altering agent which produced complete activation, all the cells had been killed by concentrations which were insufficient to cause more than 50 per cent maximal activation. Further, the evidence suggested that the catalase may be partially activated by concentrations of altering agent which cause no decrease in viability at all. Hence alteration, unlike death, may not be all-or-none per cell.

6. The fact that the biological criterion being examined was the activation of a water-soluble enzyme rules out the possibility that the reason for the logarithmic increase in altering activity with chain length was increase in concentration of the altering agent in some intracellular fat phase. It is concluded that these surface-active agents cause enzyme alteration by becoming adsorbed at some intracellular interface and thus causing, directly or indirectly, the modification of catalase properties.

7. It is considered that these data support, but do not provide critical proof for, the interfacial hypothesis, which states that catalase is present at the intracellular interface in question, but is desorbed into solution as a consequence of the alteration process.

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