Biochemistry of fermentation

Propionic acid fermentation is of major significance for the energetics of propionic acid bacteria. The main fermentation products are propionic and acetic acids and CO2 (Mashur et al., 1971 Foschino et al., 1988). Formic and succinic acids (Mashur et al, 1971) as well as acetoin and diacetyl (Tomka, 1949 Antila, 1956/57 Lee et al., 1969, 1970) are also produced, but in smaller amounts. Other volatile aromatic substances are dimethylsulfide, acetaldehyde, propionic aldehyde, ethanol and propanol (Keenan and Bills, 1968 Dykstra et al., 1971). Propionic acid fermentation differs from the other types of fermentation by the high ATP yield and by some unique enzymes and reactions. 

Propionic acid fermentation is not limited to propionibacteria it functions in vertebrates, in many species of arthropods, in some invertebrates imder anaerobic conditions (Halanker and Blomquist, 1989). In eukaryotes the propionic acid fermentation operates in reverse, providing a pathway for the catabolism of propionate formed via p-oxidation of odd-numbered fatty acids, by degradation of branched-chain amino acids (valine, isoleucine) and also produced from the carbon backbones of methionine, threonine, thymine and cholesterol (Rosenberg, 1983). The key reaction of propionic acid fermentation is the transformation of L-methylmalonyl-CoA(b) to succinyl-CoA, which requires coenzyme B12 (AdoCbl). In humans vitamin B deficit provokes a disease called pernicious anemia. 

In vertebrates, in addition to the main pathway of propionate catabolism (conversion into succinate), alternative pathways may function under conditions when the main pathway is blocked. In the termite Zootermopsis angusticollis a high Bn content apparently is due to the presence of microorganisms in the stomach (Wakayama et al., 1984). There is evidence that vitamin Bn is used by termites for the conversion of succinate to methylmalonate and incorporation of the latter instead of malonyl-CoA into methyl-branched hydrocarbons. Therefore, in termites the direction of carbon flow is the same as in bacteria (from succinate to propionate), but opposite to that found in vertebrates. From the aforesaid it is clear that studying propionic acid fermentation is important not only for understanding the biochemistry of propionic acid bacteria, but of many other organisms, including humans. 

Acetone-dried cells of P. pentosaceum can phosphorylate glucose, arabinose, glycerol and some other substrates at the expense of the phosphate group of ATP (Stone et al., 1937 Barker and Lipmann, 1949). However, the degradation of substrates is relatively insensitive to the inhibitor of glycolysis NaF, and analysis of the labeled metabolic products showed (Wood et al, 1937 Volk, 1954 Leaver et al., 1955) that the hexose monophosphate pathway also contributed to the degradation of glucose. 

The first two options are not reahzed in propionic acid bacteria, so that propionate is formed in the third reaction (Workman and Wood, 1942). This is confirmed experimentally by the ability of these bacteria to convert succinic acid into propionic acid (Wood and Workman, 1940). In animal tissues propionate and C4-acids (Flavin et al., 1955) are interconnected by the following reaction  

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Marshall, V.M.E. and Tamime, A.Y. (1997) Physiology and biochemistry of fermented milks, in Microbiology and Biochemistry of Cheese and Fermented Milk, 2nd edn (ed. B.A. Law), Blackie Academic Professional, London, pp. 153-92. 

Sanderson, G. W., Biochemistry of tea fermentation Conversion of aminoa cids to black tea aroma constituents. J. Food Sci., 35 160, 1970. 

Interpretation of the process of fermentation by yeast was one of the most controversial issues for vitalists. Its resolution was fundamental for the future development of biochemistry. In the early nineteenth century fermentation was believed to be related to putrefaction and decay. Liebig considered it to result from the breakdown of a substance (sugar) following the admission of air to the nitrogenous components in yeast juices. After the must of grape juice had fermented, the liquid cleared and the yellow sediment, yeast, was deposited. 

Piepersberg, W. Molecular biology, biochemistry, and fermentation of aminoglycoside antibiotics. In Biotechnology of Industrial Antibiotics, 2nd edition Strohl, W. R. New York Marcel-Dekker, 1997 pp. 81-163. 

Mechanism. Ochoa and his co-workers were the first to delve into the biochemistry of malo-lactic fermentation. In the late 1940 8 and the early 1950 s, Ochoa became interested in mechanisms of carbon dioxide fixation and dicarboxylic acid synthesis in higher organisms. This work... 

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