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PubMedDate not supplied

[n-Alkane oxidation by propionic acid bacteria].

Propionic acid bacteria were found for the first time to be capable of oxidizing n-alkanes. The value of QO2 is higher on a mixture of n-alkanes (C12--C20) than on individual hydrocarbons whose availability is determined by the length of a hydrocarbon chain: C15 and C16-alkanes are oxidized best of all; C14, C13 and C12-alkanes are oxidized at a lower rate; and alkanes whose chain comprises less than ten carbon atoms are not oxidized at all. Hexadecane is oxidized to CO2, cetyl alcohol and palmitic acid being intermediates; this suggests the existence of the monoterminal pathway for oxidation of n-alkanes in propionic acid bacteria.

Alkanes↗
PubMed1975

Studies of methylmalonyl coenzyme A carbonylmutase activity in methylmalonic acidemia. I. Correlation of clinical, hepatic, and fibroblast data.

Methylmalonyl-CoA carbonylmutase (mutase) activity was measured in fibroblast extracts from 15 patients with methylmalonic acidemia and in extracts of postmortem tissues from 6 of these children. Propionate oxidation and synthesis of 5-deoxyadenosylcobalamin (AdoCbl, the vitamin B12 coenzyme that is part of the mutase holoenzyme) were measured in intact fibroblasts. Mutase activity was low in the absence of added AdoCbl in fibroblast extracts from both control subjects and patients. When the assay included supplemental AdoCbl, mutase activity increased in the control subjects (to 24.0 pmol succinate/mg protein/min) and in extracts from eight of the patients (20.8 pmol/mg protein/min), but showed almost no change in extracts from the other seven patients (0.16 pmol/mg protein/min). We have defined the eight fibroblast lines that showed normal mutase activity in the presence of AdoCbl as "responsive lines" and the other seven lines as "nonresponsive." In the liver or kidney extracts of postmortem tissues, mutase activity responded to AdoCbl supplementation if fibroblast mutase activity from that patient had responded, and failed to respond if fibroblast activity failed to respond. Mean propionate oxidation in intact fibroblasts was much higher in control lines than in either responsive or nonresponsive lines (0.728 vs 0.097 vs 0.080 nmol CO2/10(6) cells/hr, respectively). AdoCbl synthesis was normal (0.27 pg AdoCbl/mg cells wet weight) in nonresponsive fibroblasts but was undetectable (less than 0.005 pg/mg cells) in the responsive lines. Thus, the deficiency of mutase activity in responsive fibroblast lines is due to the failure to synthesize significant amounts of AdoCbl, whereas the deficiency in nonresponsive lines is due to some other abnormality, presumably a defect in the mutase apoenzyme.

Animals↗
PubMed2026

Phylum-wide propionate degradation and its potential connection to poly-gamma-glutamate biosynthesis in Candidatus Cloacimonadota phylum.

The candidate phylum Cloacimonadota is frequently detected in anoxic environments such as anaerobic digestion (AD) reactors, hydrothermal vents, and deep-sea sediments, yet its metabolism remains poorly understood. Metagenomic evidence suggests capacities for amino acid fermentation, carbohydrate degradation, as well as a potential role in syntrophic propionate oxidation (SPO), a key bottleneck in AD. However, a complete methylmalonyl-CoA (mmc) pathway, central to SPO, has not been previously identified in Cloacimonadota genomes. Here, we report results from an acidified lab-scale anaerobic baffled reactor fed with sugar beet pulp, where an increase in the relative abundance of Cloacimonadota correlated with recovery of methanogenesis, resulting in increased methane content in the produced biogas. Metagenomic and metatranscriptomic analyses enabled metabolic reconstruction of the dominant Cloacimonadota operational taxonomic unit (OTU). Furthermore, using a curated database of 204 genome-resolved Cloacimonadota species, we characterized the phylum-level metabolic potential. Comparative genomics revealed alternative proteins, including 2-oxoglutarate:ferredoxin oxidoreductase and aspartate aminotransferase, likely to substitute for missing enzymes in the classical mmc pathway. These proteins were widely distributed and highly conserved across the analyzed Cloacimonadota genomes, suggesting that this variant of the SPO pathway could represent a phylum-specific trait. Moreover, we hypothesize that these alternative pathway steps may link propionate metabolism to protein degradation and poly-γ-glutamate biosynthesis. Network analysis identified the methanogenic archaeon Methanothrix as a potential syntrophic partner, an interaction further supported by propionate-fed enrichment cultures showing co-occurrence of Cloacimonadota and Methanothrix species. Our study sheds light on the Cloacimonadota metabolism, advancing our understanding of their ecological roles and potential for biotechnological applications.

Propionates↗
PubMed2026

Metagenome-resolved evidence that soluble factors in granular activated carbon-amended reactor effluent reprogram propionate metabolism and methanogenic pathways.

Granular activated carbon (GAC) enhances anaerobic digestion performance, yet the mechanisms underlying reactor-scale improvements remain incompletely understood, particularly how GAC affects biomass not attached to its surface. Here, sludge from a non-GAC up-flow anaerobic sludge blanket reactor was incubated with 0.45-&#x3bc;m-filtered effluents from non-GAC and GAC-amended reactors under repeated propionate loading, followed by genome-resolved metagenomics. GAC-reactor effluent increased methane yield from 64&#x202f;&#xb1;&#x202f;3% to 76&#x202f;&#xb1;&#x202f;3% (p&#x202f;<&#x202f;0.01) in the absence of GAC particles. A non-redundant catalog of 170 quality-filtered metagenome-assembled genomes (MAGs) was recovered, enabling pathway- and gene-set quantification. Genomic potential for both major propionate-oxidation routes increased in the GAC-effluent group relative to the non-GAC group, with a larger increase for the methylmalonyl-CoA (MMC) route than for the dismutation route (1.289- versus 1.221-fold). Accordingly, the MMC-to-dismutation preference ratio was 5.60% higher in the GAC-effluent group, alongside a broader carrier base. Cobamide potential shifted toward remodeling and cobamide-dependent use rather than increased de novo corrin-ring synthesis. Candidate electron-transfer architectures were also rebalanced: PilA-associated carriers became less prominent, whereas maturation-supported multiheme cytochrome carriers increased from 22.96% to 34.90% of community abundance, although H2/formate-module carriers remained prevalent. Quorum-sensing systems underwent pathway- and carrier-specific redistribution, while all eight curated extracellular-polysaccharide modules showed higher mean gene abundance in the GAC-effluent composite. These findings show that a filter-passing effluent fraction can extend GAC-associated effects beyond direct particle contact and link enhanced methanogenesis to a broader, redistributed network of metabolic, redox, and coordination capacities. This expands the mechanistic framework of conductive-material-assisted anaerobic digestion and provides a basis for harnessing GAC-derived functions throughout the reactor.

Extracellular polymeric substances (EPS)↗
PubMed1976

Effect of propionic acid on fatty acid oxidation and ureagenesis.

Propionic acid significantly inhibited 14CO2 production from [1-14C] palmitate at a concentration of 10 muM in control fibroblasts and 100 muM in methylmalonic fibroblasts. This inhibition was similar to that produced by 4-pentenoic acid. Methylmalonic acid also inhibited 14CO2 production from [1-14C] palmitate, but only at a concentration of 1 mM in control cells and 5 mM in methylmalonic cells. Propionic acid (5 mM) also inhibited ureagenesis in rat liver slices when ammonia was the substrate but not with aspartate and citrulline as substrates. Propionic acid had no direct effect on either carbamyl phosphate synthetase or ornithine transcarbamylase. These findings may explain the fatty degeneration of the liver and the hyperammonemia in propionic and methylmalonic acidemia.

Ammonia↗
PubMed1977

Evaluation of metabolic pathway activity in cultured skin fibroblasts and blood leukocytes.

Screening for a variety of blocked catabolic mutants can be achieved in cultured skin fibroblasts and in peripheral blood leukocytes with a simple radioisotope method that is reliable and convenient. The method measures the incorporation into trichloroacetic acid (TCA) insoluble macromolecules of a 14C-labelled intermediate in the pathway under question; incorporation of a 3H-labelled metabolite, not in the same pathway, is used as an internal control of metabolism in the cell population. The 14C/3H incorporation ratio is decreased in blocked pathways; use of the ratio method eliminates the delay required by radioautography (used in earlier adaptations of this method), the problems involved in CO2 collection, and the need to standardize cultures for cell number. This method has been used to identify cells with biochemical lesions in the oxidation of propionate, galactose, hypoxanthine and pyruvate; it has allowed us to identify a new variant of methylmalonicaciduria; we believe it can be extended to include other metabolites and pathways.

Acidosis↗
PubMed1975

Intracellular localization of hepatic propionyl-CoA carboxylase and methylmalonyl-CoA mutase in humans and normal and vitamin B12 deficient rats.

The intracellular localization of the enzymes in the vitamin B12 dependent pathway which involves the oxidation of propionate was studied in rat liver obtained from normal and vitamin B12 deficient rats as well as from man. The subcellular site of propionyl CoA carboxylase and the vitamin B12 dependent-methylmalonyl CoA mutase were determined. All of the activity of these two enzymes was demonstrated to be in the mitochondria and those enzymes were shown to be loosely bound to the inner membrane-matrix portion of the mitochondria. Vitamin B12 deficiency did not alter the subcellular localization. Finally, a rapid enzymatic assay for methylmalonyl-CoA mutase was described.

Animals↗
PubMed2026

Genome-scale insights into metabolic streamlining and photosynthetic energy balance in the extremophile green alga Picocystis salinarum (Picocystophyceae, Chlorophyta).

Picocystis salinarum is an early-diverging chlorophyte and the sole described member of the Picocystophyceae, frequently dominating hypersaline and alkaline lakes despite extreme physicochemical constraints. To elucidate the genomic foundations of its ecological success, we generated a fully annotated, chromosome-scale nuclear genome assembly of the type strain originally isolated from a saline pond in San Francisco Bay. The 18.5-Mb genome comprises 30 chromosomal assemblies, exhibits clear diploidy, and contains multiple copies of intact Ty3/Gypsy and Ty1/Copia long terminal repeat retrotransposons encoding polyproteins with atypical accessory domains. Phylogenomic analyses reveal strong affinity with the Nephroselmidophyceae. Comparative analyses reveal extensive metabolic streamlining, including the absence of a queuosine salvage pathway, the 2-methylcitrate cycle, &#x3b2;-oxidation of propionate, and branched-chain amino acid catabolism, traits retained in several marine prasinophyte lineages. In contrast, the genome preserves multiple ancestral bacterial derived systems. Notably, P. salinarum features a complete chloroplast NADH dehydrogenase-like complex, including all membrane, electron binding, and assembly components, a configuration not previously reported in sequenced chlorophyte algae. This retention implies substantial capacity for cyclic electron flow and chlororespiration, processes expected to be critical in chronically low-light and chemically extreme environments. The genome further reveals a distinctive biochemical CO2-concentrating mechanism centered on plastid-targeted phosphoenolpyruvate carboxykinase, complete plastid peptidoglycan biosynthetic and remodeling pathways, and partial retention of lipid-A-related machinery. Conversely, P. salinarum lacks canonical non-photochemical quenching proteins while retaining xanthophyll-cycle enzymes that support slower photoprotective responses. Together, these features define a coordinated genomic architecture that underpins the specialization of P. salinarum to hypersaline, alkaline, and persistently low-light ecosystems.

3&#x2010;deoxy&#x2010;D&#x2010;manno&#x2010;octulo↗
PubMed1978

Factors determining the sequence of oxidative decarboxylation of the 2- and 4-propionate substituents of coproporphyrinogen III by coproporphyrinogen oxidase in rat liver.

Coproporphyrinogen oxidase (EC 1.3.3.3) catalyses the oxidative decarboxylation of the 2- and 4-propionate substituents of coproporphyrinogen III to form protoporphyrinogen IX. A 4-propionate-substituted porphyrinogen, harderoporphyrinogen, which is also a substrate for coproporphyrinogen oxidase, is formed during the reaction. Synthetic [(14)C]coproporphyrinogens III, specifically labelled in the carboxyl carbon atoms of either the 2- or 4-propionate substituents, were used to measure the rate of decarboxylation of each substituent by rat liver coproporphyrinogen oxidase. The experimental results, together with the recognition that in all known substrates of coproporphyrinogen oxidase only those propionate groups flanked by a specific arrangement of substituents are decarboxylated, indicate that the 4-propionate group of coproporphyrinogen III cannot be attacked until the 2-propionate group has been decarboxylated. Production of (14)CO(2) from the substrate labelled in the 2-propionate group therefore measures the formation of harderoporphyrinogen, whereas (14)CO(2) from the 4-propionate-labelled substrate measures protoporphyrinogen IX formation. The rate of harderoporphyrinogen formation is about twice that of protoporphyrinogen, and this ratio is unchanged by varying the concentration of coproporphyrinogen III or by competitive inhibition of the enzyme. When coproporphyrinogen III is present in an excess, two fractions of harderoporphyrinogen can be distinguished. One accumulates during the reaction, and the other, which is destined to become protoporphyrinogen IX, does not equilibrate with added harderoporphyrinogen. It is suggested that both decarboxylations take place at the same active centre, which becomes temporarily inaccessible to coproporphyrinogen III and added harderoporphyrinogen, and that the molecule rotates after the first decarboxylation to allow the second to take place.

Animals↗
PubMed1978

[Microphotometric study of the activity of oxidative enzymes in the endometrial epithelium of rats following ovariectomy and administration of testosterone propionate].

A method of comparative microphotometry was applied to the study of the oxidative enzymes in the epithelial lining of the uterine cavity and the glandular epithelium of the ovariectomized rats during the climacteric disturbances. There was an increase in the activity of lactic dehydrogenase (LDH) and glucose-6-phosphoric dehydrogenase (G-6-PDH) and a fall of the succinic dehydrogenase (SDH) and NAD- and NADP-diaphorases activity in the cells of the epithelial lining the uterine cavity. The glandular epithelium displayed an elevation of the LDH activity and a sharp fall of the SDH, NAD- and NADP-disphorases activity. Administration of testosterone-propionate caused an marked elevation of the activity of the oxidative enzymes in the epithelium of the rat endometrium in comparison with level of their activity in control animals and rats given no hormone.

Animals↗
PubMed1978

Kinetic parameters and relative turnovers of some important catabolic reactions in digesting sludge.

The kinetics of propionate degradation, acetate splitting, and hydrogen consumption in digesting sludge were investigated in a lab-scale digester. At natural steady-state conditions, the acetate-splitting systems in well-digested sludge were about half saturated. Propionate-degrading systems were saturated to only 10 to 15%, and hydrogen removal was less than 1% of the maximum possible rate. It was concluded that acetate splitting rather than "methanogenesis from fatty acids" is the rate-limiting reaction in the anaerobic degradation of dissolved organic matter and that a methoanogenic anaerobic ecosystem is stabilized by its large unused capacity of hydrogen consumption which is "buffering" the partial pressure of dissolved hydrogen in the system at sufficiently low values to permit rapid fatty acid oxidation. A tentative scheme of the substrate flow in sludge digestion is presented. It suggests that acid formation coupled with hydrogen formation via pyridine dinucleotide oxidation yields the immediate substrates, namely acetate and hydrogen, for about 54% of the total methanogenesis.

Acetates↗
PubMed1975

Influence of nitrate on fermentation pattern, molar growth yields and synthesis of cytochrome b in Propionibacterium pentosaceum.

Under anaerobic conditions, Propionibacterium pentosaceum reduces nitrate to nitrite until nitrate is exhausted from the medium when nitrite is converted into N2 or N2O. In the presence of nitrate, fermentation patterns for lactate, glycerol and pyruvate were different from those obtained during anaerobic growth without an inorganic electron acceptor. In the presence of these substrates, a drastic decrease in propionate formation was observed, some pyruvate accumulated during growth with lactate, and acetate was produced from glycerol. Acetate production from lactate and pyruvate was not influenced by the presence of nitrate. Furthermore, CO2 was produced by citric acid cycle activity. The fermentation pattern during nitrite reduction resembled that of P. pentosaceum grown anaerobically without an inorganic electron acceptor. Nitrits has a toxic effect, since bacteria inoculated into a medium with 9 mM-nitrite failed to grow. The cytochrome spectrum of anaerobically grown P. pentosaceum was similar with and without nitrate. In membrane fractions of bacteria grown anaerobically with nitrate, cytochrome b functioned in the transfer of electrons from lactate, glycerol I-phosphate and NADH to nitrate. Molar growth yeilds were increased in the presence of nitrate, indicating an increased production of ATP. This could be explained by citric acid cycle activity, and by ocidative phosphorylation coupled to nitrate reduction. Assuming that I mol ATP is formed in the electron transfer from lactate or glycerol I-phosphate to nitrate, and that 2 mol ATP are formed in the electron transfer from NADH to nitrate, YATP values (g dry wt bacteria/mol ATP) were obtained of between 5-0 and 12-6. The higher YATP values were similar to those obtained during anaerobic growth without an inorganic electron acceptor. This supports the assumptions about the efficiency of oxidative phosphorylation for electron transport to nitrate. Low YAPT values were found when high concentrations of nitrite (15 to 50 mM) accumulated, and were probably due to the toxic effect of nitrite.

Acetates↗
PubMed2022

Direct anabolic metabolism of three-carbon propionate to a six-carbon metabolite occurs in&#xa0;vivo across tissues and species.

Anabolic metabolism of carbon in mammals is mediated via the one- and two-carbon carriers S-adenosyl methionine and acetyl-coenzyme A. In contrast, anabolic metabolism of three-carbon units via propionate has not been shown to extensively occur. Mammals are primarily thought to oxidize the three-carbon short chain fatty acid propionate by shunting propionyl-CoA to succinyl-CoA for entry into the TCA cycle. Here, we found that this may not be absolute as, in mammals, one nonoxidative fate of propionyl-CoA is to condense to two three-carbon units into a six-carbon trans-2-methyl-2-pentenoyl-CoA (2M2PE-CoA). We confirmed this reaction pathway using purified protein extracts provided limited substrates and verified the product via LC-MS using a synthetic standard. In whole-body in&#xa0;vivo stable isotope tracing following infusion of 13C-labeled valine at steady state, 2M2PE-CoA was found to form via propionyl-CoA in multiple murine tissues, including heart, kidney, and to a lesser degree, in brown adipose tissue, liver, and tibialis anterior muscle. Using ex&#xa0;vivo isotope tracing, we found that 2M2PE-CoA also formed in human myocardial tissue incubated with propionate to a limited extent. While the complete enzymology of this pathway remains to be elucidated, these results confirm the in&#xa0;vivo existence of at least one anabolic three- to six-carbon reaction conserved in humans and mice that utilizes propionate.

Acetyl Coenzyme A↗
PubMed1979

Kinetic and mechanistic studies on the reduction of melilotate hydroxylase by reduced pyridine nucleotides.

The reduction of the melilotate hydroxylase . 2-OH-phenyl propionate complex by NADH and reduced 3-acetyl pyridine adenine dinucleotide (AcPyNADH) has been investigated using steady state kinetic and rapid reaction techniques. Reduction by NADH appeared to involve only one charge-transfer-type intermediate (between reduced enzyme and NAD) as previously described (Strickland, S., and Massey, V. (1973) J. Biol. Chem. 248, 2953-2962). Reduction by AcPyNADH was shown to involve two charge-transfer-type intermediates. The first was between oxidized enzyme and AcPyNADH and the second was between reduced enzyme and AcPyNAD. Reaction of AcPyNADH with oxidized enzyme . 2-OH-phenyl propionate complex to form the first charge-transfer complex reached equilibrium within the mixing time of the stopped flow apparatus (5 ms). Subsequent steps in the reaction appeared to be first order and were independent of the AcPyNADH concentration. An 8-fold deuterium isotope effect on the step involving flavin reduction was found when reduced 3-acetyl[4A-2H]pyridine adenine dinucleotide (AcPyNADD) was used as the reductant. Analysis of the rapid reaction results for the reaction of oxidized pyridine nucleotide with reduced enzyme . 2-OH-phenyl propionate complex indicated the presence of two forms of reduced enzyme (in equilibrium) of which only one form was capable of reacting with the oxidized pyridine nucleotide. Based on the rapid reaction data, a mechanism for the reduction half-reaction is proposed. The turnover number calculated from this mechanism is in good agreement with that determined from the steady state data.

Electron Transport↗