The properties of factors present in boiled yeast juice which stimulate the oxidative breakdown of citrate in baker's yeast have been investigated. The activity has been shown to reside predominantly in the nucleotide fractions (i.e., pyridine codehydrogenases) and to a lesser extent in the ammonium salts present in whole yeast cells. The activity of the Citrate Oxidation Factor (COF) concentrated from yeast extracts and described by Foulkes (Biochem. J. 54 323 (1953)) was attributable entirely to the ammonium content of COF preparations. This activating effect of ammonium ions is accompanied by their removal from the assay system and the simultaneous production of glutamic acid. Correlation of the uptake of ammonium ion with the increased citrate metabolism indicates that the activity of the ammonium salts lies in their ability to promote the reductive amination of α-oxoglutarate. The mechanism(s) whereby this serves to stimulate the further breakdown of citrate to oxoglutarate involves the mediation of the pyridine codehydrogenases (DPN, TPN). These findings are discussed in relation to the known functioning of individual stains of the tricarboxylic acid cycle and to possible alternative pathways for the oxidation of citrate in yeast.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:672137 |
| Date | January 1955 |
| Creators | Whitehouse, M. W. |
| Contributors | Kent, Paul Welberry |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:51368866-76d0-49aa-afa5-70d0888ea3c9 |
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