The effect of cyanide on the respiration of animal tissues

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Abstract
A study has been made of the effect of various concentrations of cyanide on the rates of respiration of a number of animal tissues. In most cases a cyanide concentration of M/1000 is sufficient to produce maximum inhibition. No greater inhibition is produced by increasing the cyanide concentration 100 times. Maximum inhibition varies in different tissues between 40% and 90%, the average value being about 60%. It is concluded that the respiration of animal tissues is of 2 sorts. One, accounting for about 2/3of the total, is due to systems poisoned by cyanide; the other 1/3 is due to systems which resist cyanide. Warburg''s "respiratory enzyme" (Keilin''s cytochrome-indophenol-oxidase system) can therefore only account at most for about f of the total respiration of animal tissues. The respiration of spleen, unlike that of all the other tissues tested, is not affected by small amounts (Af/1000) of cyanide. It appears to contain some substance with a greater affinity for cyanide than the "respiratory enzyme." Negelein''s statement that the respiration of yeast is almost completely inhibited by cyanide is confirmed. Some samples of yeast, however, show an incomplete (85%) inhibition. The effect of pyrophosphate on the respiration rates of liver, muscle and yeast has also been studied. With liver, small concentrations produce a slight acceleration, but larger amounts produce inhibitions which vary between 30% and 70% but are always considerably less than the corresponding cyanide inhibitions. With muscle pyrophosphate produces a greater inhibition than cyanide Pyrophosphate produces no effect on yeast. Possibly the cell-membranes are not permeable to it. Since the "respiratory enzyme" is not inhibited by pyrophosphate, the inhibition of respiration must be due to its action on some other system. It is shown that pyrophosphate inhibits the reduction of methylene blue by the succinoxidase system, though this reaction is unaffected by cyanide. The actions of both cyanide and pyrophosphate on respiration are reversible.

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