Biological synthesis of oxaloacetic acid from pyruvic acid and carbon dioxide

Publisher Website
Google Scholar
Abstract
The 6 strains of propionic acid bacteria examined readily reduce oxaloacetate to succinate. Fumarate and [iota]([long dash])-malate are formed as intermediate metabolites. The H required for the reduction of oxaloacetate can be supplied by several reactions, e.g., the conversion of pyruvate into acetate. Fumarate and [iota]([long dash])-malate are readily reduced to succinate by Propionibacterium shermanii. A powerful fumarase is present in P. shermanii. The rates of succinate formation from oxaloacetate, fumarate and malate are sufficiently high to allow the assumption that these acids are intermediates in the formation of succinate from glycerol, in accordance with scheme (2). Fumarate is formed when glycerol is anaerobically fermented by P. shermanii. Fumarate, malate or oxaloacetate catalytically accelerate the fermentation of glycerol; thus these acids act as intermediary H carriers in the fermentation of glycerol. The expts. of Carson and Ruben with radioactive C support this view. Similar catalytic effects of oxaloacetate were observed when manni-tol, inositol, arabinose or erythritol were the substrates of fermentation. The view that succinate is synthesized in propionic acid bacteria from 2 mol. of acetate is rejected. Acetate can be oxidized aerobically, and probably anaerobically, to form CO2. The oxidative conversion of acetate into CO2 explains the low yields of acetate observed by previous investigators. The facts concerning the synthesis of succinate by propionic acid bacteria are explained on the assumption that synthesis of oxaloacetate from pyruvate and CO2 is the primary step in the synthesis of the 4-carbon chain.