Propionate catabolism

A natural question is "Why has this complex pathway evolved to do something that could have been done much more directly " One possibility is that the presence of too much malonyl-CoA, the product of the P oxidation pathway of propionate metabolism (Fig. 17-3, pathways a and c), would interfere with lipid metabolism. Malonyl-CoA is formed in the cytosol during fatty acid biosynthesis and retards mitochondrial P oxidation by inhibiting carnitine palmitoyltransferase i.46 70a 75 However, a relationship to mitochondrial propionate catabolism is not clear. 

Halamkar P. P., Heisler C. R. and Blomquist G. J. (1986) Propionate catabolism in the housefly Musca domestica and the termite Zootermopsis nevadensis. Insect Biochem. 16, 455-461. 

Much interest has been shown in the biosynthesis of insect juvenile hormones (62 R1, R2 = Me or Et). In adult male moths, [l-14C]propionate was specifically incorporated into juvenile hormone I [JH-1, (62 R1 = R2 = Et)], and tracer was only found at, and equally distributed between, C-7 and C-ll.90 Application of [2-14C]-and [3-14C]-propionate led to extensive randomization of label, which suggests that C-2 and C-3 formed in propionate catabolism can be re-used as smaller fragments, whilst C-l is either removed from propionate in a metabolically active form or is highly diluted. Ternary complexes of brain, corpora cardiaca, and corpora allata from the tobacco budworm Heliothis virescens produced labelled JH-I and JH-II (62 R1 = Et, R2 = Me) when incubated with L-[Me-14C]methionine or sodium [l-l4C]propionate.91 Partial degradation of the juvenile hormones showed that in JH-I portions a and /3 (62) had incorporated one atom of tracer from each propionate, whereas fraction y was unlabelled, and in JH-II only fraction a was... 

Vitamin B.. is a required cofactor for methylmalonyl-CoA mutase, which is involved in propionate catabolism in mammals. This fact and the differences observed in the precursors to propionate and methylraalonate among insect species (Table I) prompted an examination of a number of insects for vitamin Bj levels. The termite Z. angusticollis, which readily converts succinate to methylmalonate, has large amounts of vitamin B.., whereas the American cockroach has low levels and the housefly does not have detectable amounts of vitamin B1 (10). Thus, both dietary considerations and levels of vitamin may play a role in determining the precursors to propionyl and methylmalonyl derivatives in insects. 

A pathway for converting propionate to acetate is not unique in biological systems. Plants, many of which apparently do not contain vitamin B, convert propionate directly to acetate via a 3-hydroxypropionate intermediate (22). The finding that many insects either do not have detectable levels of B. or have very low levels (10) suggests that, like plants, insects have evolved an alternative route of propionate catabolism. The conversion of propionate to acetate may be a general pathway in insects, as even the termite Z, angustlcollis, which has large amounts of vitamin B.. , bas this pathway. 

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. 

Plassmeier J, Persicke M, Ptihler A, Sterthoff C, Riickert C, Kalinowski J (2012) Moleculeu- characterization of PrpR, the transcriptional activator of propionate catabolism in Corynebacterium glutamicum. J Biotechnol 159 1-11... 

The propionate metabolism in higher plant tissues has already been studied by Stumpf and coworkers (5,6) and a pathway for propionate catabolism has been proposed (6,7). This pathway (modified (5-oxidation) has been supported by data published recently (8). However, of the intermediates and end products of the proposed pathway none of the acyl-CoAs has been demonstrated so far. 

Methylmalonyl CoA mutase, leucine aminomutase, and methionine synthase (Figure 45-14) are vitamin Bj2-dependent enzymes. Methylmalonyl CoA is formed as an intermediate in the catabolism of valine and by the carboxylation of propionyl CoA arising in the catabolism of isoleucine, cholesterol, and, rarely, fatty acids with an odd number of carbon atoms—or directly from propionate, a major product of microbial fer-... 

Horswill AR, JC Escalande-Semerena (1999) Salmonella typhimurium LT2 catabolizes propionate by the 2-methylcitric acid cycle. J Bacterial 181 5615-5623. 

Kosaka T et al. (2006) Reconstruction and regulation of the central catabolic pathway in the thermophilic propionate-oxidizing syntroph Pelotomaculum thermopropionicum. J Bacterial 188 202-210. 

The oxidation of aciy lic acid can be rationalized in terms of the endogenous catabolism of propionic acid, in which acrylyl coenzyme A is an intermediate. This pathway is analogous with fatty acid 3-oxidation, common to all species and, unlike the corresponding pathway in plants, does not involve vitamin 8,2. 3-Hydroxypropionic acid has been found as an intennediate in the metabolism of acrylic acid in vitro in rat liver and mitochondria (Finch Frederick, 1992). The CO2 excreted derives from the carboxyl carbon, while carbon atoms 2 and 3 are converted to acetyl coenzyme A, which participates in a variety of reactions. The oxidation of acrylic acid is catalysed by enzymes in a variety of tissues (Black Finch, 1995). In mice, the greatest activity was found in kidney, which was five times more active than liver and 50 times more active than skin (Black et al., 1993). 

For this group of aminomutases PLP is required as a second coenzyme. Third, X is attached via a carbon atom the enzymes are called mutases. Methyl-malonyl-Co mutase is required for catabolism of propionate in the human body, and is one of only two known vitamin B12-... 

Figure 17-3 Catabolism of propionate and propionyl-CoA. In the names for methylmalonyl-CoA the R and S refer to the methylmalonyl part of the structure. Coenzyme A is also chiral.

On the other hand, the tacking on of an extra C02 and the use of ATP at the beginning suggests that the methylmalonyl-CoA pathway (Fig. 17-3) is a biosynthetic rather than a catabolic route (see Section H,4). The methyl-malonyl pathway provides a means for converting propionate to oxaloacetate, a transformation that is chemically difficult. 

Testosterone Propionate, Winstrol Depot, Durabolin, Deca Durabolan, even Parabolan if I could find it. I stacked one or more of these together with the rest of my cycle gear and added an AAS that worked well in a catabolic environment, preferably Primobolan Depot. 3 weeks with high AAS dosages was my max for site injection. 

These investigations have shown that cestodes, in common with other parasitic helminths, utilise carbohydrate as the major, and possibly only, energy substrate. In addition, carbohydrate catabolism in cestodes is characterised by the excretion of reduced end-products (e.g. lactate, propionate, succinate) even under aerobic conditions. 

Insects have an unusual pathway for catabolizing propionate which may be related to the absence or low levels of vitamin found in many species. The propionate to acetate pathway is present in all insects which have been studied, including the termite, which has high levels of vitamin B1 . The presence of this unusual metabolic pathway for propionate metabolism offered the potential for selectivity in developing insect control... 

The primary fate of dietary fibers is digestion and catabolism by the gut microflora to short-chain fatty acids and carbon dioxide. The major products of this microbiai mctaboiism — acetic, propionic, and butyTic acid — are important sources of energy for ruminants (sheeps cows). Dietary fiber is retained in a chamber of their gastrointeslinai tracts, calied the rumen, where it is converted to short-chain fatty acids by the gut micro flora. The fatty acids produced may supply 3 75 y<> of the energy requirement of the ruminant. 

It has been established that propionate and the longer fatty acids are catabolized by similar syntrophic associations (Boone and Bryant, 1980). 

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