Chemical Nature of the Oxygen-transferring Ferment of Respiration in Plants.

The effect of carbon monoxide on the respiration of animal cells and aerobic bacteria (10), and on anaerobic butyric acid fermentation (6), has shown that the ferments which act as catalysts in these energy-yielding cellular processes are compounds of heavy metals: for carbon monoxide reacts at low temperatures only with heavy metals, and respiration as well as anaerobic butyric acid fermentation is stopped at low temperatures by carbon monoxide (6, 10). It has been further shown that these catalysts of respiration and of the anaerobic butyric acid fermentation are compounds of iron: for, of all the combinations of carbon monoxide with heavy metals only those with iron are dissociated by visible light, and the cell which in the presence of carbon monoxide stops respiring or forming butyric acid, recommences its metabolic reactions when irradiated by light (7, 10, 11). Two iron ferments, the oxygen-transferring ferment of respiration and the anaerobic-splitting ferment, are apparently in too small a concentration and are too unstable to be isolated from the living cells by the usual methods of analytical chemistry. By combining them with carbon monoxide and by measuring the various degrees of dissociation' of the ferment-CO combinations (by the increase of the respiration or of the anaerobic-splitting metabolism when irradiated by different wave lengths of visible light) an indirect method was found for examining the ferments and determining their absorption spectra, their "color," within the structure of the living cell, as it were, without separating them chemically from the other cellular substances. After the absorption spectrum of the ferment-CO combination had once been found, it was possible to compare it with the absorption spectra of substances which are accessible and can be analyzed by the ordinary methods of chemistry. In this way WARBURG (12) discovered that the constitution of the oxygen-transferring ferment of respiration in animal body cells and aerobic bacteria was phaeohaemin. Neither alcohol fermentation nor lactic acid fermentation can be affected by carbon monoxide (11), and according to WARBURG and CHRISTIAN (13) "there are also oxidation processes which are insensitive to carbon monoxide as in Chlorella, yeast press juice and anaerobic bacteria." From these anaerobic bacteria it was possible to separate a catalytically active substance,