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Terminal respiration in pseudomonas aeruginosa Smith, Roberts Angus

Abstract

The conventional tricarboxylic acid cycle is generally accepted as the sole means of terminal respiration in aerobic micro-organisms. Cell-free extracts of Pseudomonas aeruginosa were found to contain the condensing enzyme and were able to oxidize all the intermediates of the conventional tricarboxylic acid cycle. In spite of this evidence in favour of the conventional tricarboxylic acid cycle some deviations from the normal scheme were found. Even though an ability to oxidize isocitrate was noted the cell-free extracts had no ability to equilibrate isocitrate with citrate, indicating possession of an impaired aconitase system. Furthermore, when citrate was used as substrate all attempts to isolate alpha-Ice toglutarate in the fermentation liquor failed. Moreover, the 2,4, dinitrophenylhydra-zone of glyoxylate was easily isolated in relatively large quantities when either citrate or cis-aconitate were used as substrates. Although glyoxylate was never isolated when isocitrate was used as substrate it was produced from citrate or cis-aconitate under either aerobic or anaerobic conditions. Since the reaction proceeded in the presence or absence of oxygen it was assumed to be a hydrolytic cleavage of cis-aconitate. In addition to glyoxylate, succinate was found as a product of the anaerobic degradation of citrate or cis-aconitate and in the presence of the cell- extract citrate was readily formed by synthe-i sis from glyoxylate and succinates Succinate was then shown to be oxidized by P.aeruginosa through fumarate and 1-malate to oxalacetate, indicating a similarity to the tricarboxylic acid cycle. These results represent a deviation from the conventional tricarboxylic acid cycle and show that the fragmentary evidence normally accepted is not sufficient to prove the presence of a conventional tricarboxylic acid cycle.

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