ON THE OXIDATION OF FATTY ACIDS BY PURPLE BACTERIA

II. THE FATE OF ACETATE AND PROPIONATE IN RESPIRATION AND PHOTOSYNTHESIS

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1. Using a non-sulfur purple bacterium, Rhodobacillus palustris, the availability of various fatty acids as the hydrogen donor for the photosynthetic CO₂ reduction was investigated. The oxidation velocity of each fatty acid, as it is reflected in the rate of CO₂-uptake, was found to be constant up to a very low concentration of the acid, indicating
that the Michaelis' constant of the reactions are appreciably small. The rate at saturating concentration of substrate increased with the number of carbon atom in the acid molecule up to C₉, and then gradually de-creased till it became zero at C₁₇-C₁₈. The ratio: (net CO₂-uptake in mole)/(fatty acids used in mole) also increased with the number of the carbon atom in the acid molecule. These findings are essentially similar to those made previously in the comparative study of the avail-ability of various fatty acids as substrate of respiration by the same organism. A distinct difference lies, however, in the fact that the photo-synthetic activity of bacterial cells is markedly suppressed by the effect of higher fatty acids which could be readily used as the substrate of res-piration.
2. Per Oxidation of one mole each of acetate and propionate, 0.24 and 0.49 moles, respectively, of CO₂ were reduced photosynthetical. ly. Previous experiments showed that in the respiratory process these acids were oxidized with the consumption of 0.5 and 1.0 moles, respective-ly, of O₂ and indeed without the, formation of CO₂
3. Attempt was made to identify qualitiatively the products formed from acetate and propionate in the process of respiration and photo-synthesis. It was found that in respiration succinate, probably ac-companied by fumarate was formed from acetate, and lactate and pro-bably pyruvate from propionate. On the other hand, the products formed in photosynthesis were found to be succinate from acetate and lactate from propionate.
4. These data were interpreted as indicating that the pathway of fatty acid oxidation by the organism tested is essentially the same in photosynthesis and respiration, and that acetate and propionate are oxidized according to the following fromulae:
Acetate^-H→1/2 Fumarate
Propionate^-H→(Acrylate)^+H₂O→Lacatate^-2H→Pyruvate
It is my great pleasure to thank Prof. Dr. H. Tamiya for his kind guidance and encouragement throughout this work. This work was supported by a grant from the Scientific Research Fund of the Ministry of Education which is gratefully acknowledged