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Interactions of acetate, propionate and butyrate in sheep liver mitochondria.

ABSTRACT: 1. Interactions in the rates of consumption of acetate, propionate and butyrate in sheep liver mitochondria were examined in the presence and absence of l-malate and alpha-oxoglutarate. 2. Acetate was not consumed in absence of ancillary substrate but utilization of acetate (7.2nmol/min per mg of protein) occurred in the presence of alpha-oxoglutarate. This consumption was abolished by propionate or butyrate but the presence of acetate did not affect consumption of propionate or butyrate. 3. Propionate consumption (10.1nmol/min per mg of protein) was unaffected by malate but was stimulated by 63% by butyrate or by 180% by alpha-oxoglutarate. 4. Butyrate consumption (3.3nmol/min per mg of protein) was stimulated by 117% by malate, by 151% by propionate and by 310% by alpha-oxoglutarate. 5. In the absence of ancillary substrates the maximum rate of total volatile fatty acid utilization (24.7nmol/min per mg of protein) occurred with a mixture of propionate and butyrate. When both propionate and butyrate were present total consumption was not affected by malate but was stimulated by 24% by alpha-oxoglutarate. With alpha-oxoglutarate present, propionate and butyrate each decreased the other's consumption by about 26%, but the total utilization was the greatest observed. 6. The inhibition of acetate consumption by propionate or butyrate is unexplained, but the remaining effects are consistent with an interaction of propionate and butyrate through oxaloacetate together with a general limitation imposed by a need for GTP to rephosphorylate AMP formed during activation of the volatile fatty acids.

SUBMITTER: Smith RM

PROVIDER: S-EPMC1177274 | biostudies-other | 1971 Oct

REPOSITORIES: biostudies-other

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Project description:1. Metabolism of propionate by sheep-liver mitochondria was stimulated catalytically by alpha-oxoglutarate, pyruvate, citrate and isocitrate. Succinate was stimulatory at higher concentrations, but fumarate and malate were inert. These effects were all independent of the presence of ATP, succinate being less effective when ATP was present. 2. Compared with the metabolism of added succinate, propionate metabolism was resistant to malonate inhibition, but only in the presence of added ATP. In the absence of ATP propionate metabolism was more sensitive to malonate inhibition than was the metabolism of succinate. 3. In the absence of malonate, and at malonate concentrations in the range 5-100mm, alpha-oxoglutarate increased the rate of fixation of [2-(14)C]propionate by about 50% without altering the nature of the fixation products. 4. Metabolism of [1-(14)C]-propionate in the presence of 50mm-malonate was accompanied by accumulation of about half the propionate consumed as succinate. When alpha-oxoglutarate was present in addition part of the alpha-oxoglutarate was metabolized and the rate of propionate consumption was increased. The total succinate that accumulated corresponded to the alpha-oxoglutarate consumed plus about half the propionate metabolized. 5. When [1-(14)C]propionate was metabolized in the absence of malonate about 70% of the generated succinate was oxidized to fumarate or beyond. The addition of malonate decreased the rate of propionate metabolism, and decreased to about half the fraction of generated succinate oxidized. 6. When propionate and 10mm-succinate were metabolized together, the total oxidation of succinate was greater than that with 10mm-succinate alone. The increment in succinate oxidation corresponded to about half the propionate metabolized in the presence or absence of malonate or ATP. 7. It is suggested that the metabolism of propionate is specifically limited by the rate of oxidation of the generated succinate, and that the succinate oxidase concerned is distinct from that responsible for the oxidation of added succinate. 8. The results are discussed in terms of the mode of action of certain stimulants and inhibitors of propionate metabolism. It is suggested that many of these act by stimulation or inhibition of the specific succinate oxidase that limits propionate metabolism.

Project description:1. A study has been made of the effects of ATP and alpha-oxoglutarate on the rate of metabolism of propionate by whole mitochondria from sheep liver, and by mitochondria disrupted with ultrasonic energy or by freezing and thawing. Whole mitochondria metabolized propionate aerobically; the rate was increased and stabilized by 0.5mm-ATP, and increased at least a further 50% by 1.67mm-alpha-oxoglutarate. 2. Anaerobically, externally added ATP at high concentrations permitted slow consumption of propionate. 3. In the presence of 1.3mm-ATP, but in the absence of alpha-oxoglutarate, there was no significant lag phase in the removal of propionate by whole mitochondria, and the rate declined at concentrations below 2mm. In the additional presence of 1.67mm-alpha-oxoglutarate or -glutamate, propionate was removed at linear rates until the residual propionate concentration was about 0.1mm. 4. Maximum rates of metabolism of propionate by whole mitochondria with 1.3mm-ATP occurred with alkali-metal chloride concentrations of 65-95mm and with K(+)/Na(+) ratios 5-10, both in the presence and absence of alpha-oxoglutarate. 5. With disrupted mitochondria stimulatory effects of alpha-oxoglutarate were obtained only aerobically, only with propionate and not propionyl-CoA as substrate, and only when sufficient mitochondrial structure remained to permit unsupplemented metabolism of propionate to occur. 6. In the presence of ATP and CoA, disrupted mitochondria fixed [2-(14)C]propionate at a rate adequate to explain the rate with whole mitochondria stimulated with ATP and alpha-oxoglutarate. 7. With both whole and partially disrupted mitochondria in the absence of ATP, the rate of metabolism of propionate was inhibited by about 80% by 3.3mm-AMP. The inhibition was partly overcome by alpha-oxoglutarate plus CoA. 8. It is concluded that the ultimate effect of alpha-oxoglutarate was to increase the rate of supply of ATP within the mitochondria. Reasons are given why it is premature to conclude that the extra ATP arose entirely from the oxidation of alpha-oxoglutarate itself.

Project description:Microbial inhibition by high ammonia concentrations is a recurring problem that significantly restricts methane formation from intermediate acids, i.e., propionate and acetate, during anaerobic digestion of protein-rich waste material. Studying the syntrophic communities that perform acid conversion is challenging, due to their relatively low abundance within the microbial communities typically found in biogas processes and disruption of their cooperative behavior in pure cultures. To overcome these limitations, this study examined growth parameters and microbial community dynamics of highly enriched mesophilic and ammonia-tolerant syntrophic propionate and acetate-oxidizing communities and analyzed their metabolic activity and cooperative behavior using metagenomic and metatranscriptomic approaches. Cultivation in batch set-up demonstrated biphasic utilization of propionate, wherein acetate accumulated and underwent oxidation before complete degradation of propionate. Three key species for syntrophic acid degradation were inferred from genomic sequence information and gene expression: a syntrophic propionate-oxidizing bacterium (SPOB) "Candidatus Syntrophopropionicum ammoniitolerans", a syntrophic acetate-oxidizing bacterium (SAOB) Syntrophaceticus schinkii and a novel hydrogenotrophic methanogen, for which we propose the provisional name "Candidatus Methanoculleus ammoniitolerans". The results revealed consistent transcriptional profiles of the SAOB and the methanogen both during propionate and acetate oxidation, regardless of the presence of an active propionate oxidizer. Gene expression indicated versatile capabilities of the two syntrophic bacteria, utilizing both molecular hydrogen and formate as an outlet for reducing equivalents formed during acid oxidation, while conserving energy through build-up of sodium/proton motive force. The methanogen used hydrogen and formate as electron sources. Furthermore, results of the present study provided a framework for future research into ammonia tolerance, mobility, aggregate formation and interspecies cooperation.

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Interactions of acetate, propionate and butyrate in sheep liver mitochondria.

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