The effect of fumarate on respiration

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Abstract
For mano-metric determinations of the respiration rate of pigeon breast and pig heart muscle, Ringer buffered with M/60 phosphate proved a more satisfactory medium than plain phosphate. Fumarate addition stabilized the respiration at the existing rate; an increase was apparent only by comparison with the control, in which the respiratory rate falls off. Succinate, malate and oxalacetate, which yield fumarate in contact with tissue, duplicated the fumarate effect. A heat-stable, dialysable substance in muscle extract increased the respiration, as did co-enzyme and co-ferment to a much lesser extent. The extract substance is not succinate, since the latter changes the R. Q. from its normal value of about 0.9 to 0.5, while the former does not affect the R. Q. Fumarates in low concentration act catalytically, the increase in respiration being 6-10 times greater than could be accounted for by the total oxidation of the fumarate added, the R. Q. remaining normal, and small amounts of fumarate being still detectable after prolonged contact with respiring tissue. Greater concentrations of fumarate change the R. Q., so that the increased resp. in this case is due partly to the catalytic effect, partly to oxidation of fumarate.

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