Succinic acid turnover and propionate production in the bovine rumen

High velocity constants for conversion of added succinate to propionate, together with estimations of pool size, showed that extracellular succinate is the major precursor of the propionate formed in the rumen. Some bacteria give off succinate as a final fermentation product which is decarboxylated by others to propionate.

EFFECT IN THE COW OF INTRARUMINAL INFUSIONS OF VOLATILE FATTY ACIDS AND OF LACTIC ACID ON THE SECRETION OF THE COMPONENT FATTY ACIDS OF THE MILK FAT AND ON THE COMPOSITION OF BLOOD

1. The effects in the cow of intraruminal infusions of acetic acid, propionic acid or butyric acid on the secretion of the component fatty acids of the milk fat, and of these acids and of lactic acid on the composition of the blood plasma of the jugular vein, have been studied. 2. The infusion of acetic acid or butyric acid increased the yield of the C(4)-C(16) acids of milk fat but decreased the yield of C(18) acids. The infusion of propionic acid decreased the yields of all major component acids except palmitic acid and possibly lauric acid. 3. The changes in the concentrations in blood plasma of glucose and of ketone bodies were consistent with the glucogenic effect of propionic acid and the ketogenic effects of butyric acid and acetic acid. The effects of lactic acid were not consistent from cow to cow. Only with the infusion of acetic acid was a significant increase in the concentration of total volatile fatty acids in blood plasma found. Infusions of butyric acid and of propionic acid tended to depress the concentration of citric acid in the blood plasma and infusion of acetic acid increased it. No consistent effects of the infused acids on the concentration in blood plasma of esterified cholesterol, free cholesterol, triglyceride or phospholipid were observed. 4. The possibility is discussed that the effects of the infused acids on milk-fat secretion are caused through an alteration of the concentrations of precursors of milk fat in mammary arterial blood.

THE OXIDATION OF D- AND L-GLYCERATE BY RAT LIVER

1. The interconversion of hydroxypyruvate and l-glycerate in the presence of NAD and rat-liver l-lactate dehydrogenase has been demonstrated. Michaelis constants for these substrates together with an equilibrium constant have been determined and compared with those for pyruvate and l-lactate. 2. The presence of d-glycerate dehydrogenase in rat liver has been confirmed and the enzyme has been purified 16-20-fold from the supernatant fraction of a homogenate, when it is free of l-lactate dehydrogenase, with a 23-29% recovery. The enzyme catalyses the interconversion of hydroxypyruvate and d-glycerate in the presence of either NAD or NADP with almost equal efficiency. d-Glycerate dehydrogenase also catalyses the reduction of glyoxylate, but is distinct from l-lactate dehydrogenase in that it fails to act on pyruvate, d-lactate or l-lactate. The enzyme is strongly dependent on free thiol groups, as shown by inhibition with p-chloromercuribenzoate, and in the presence of sodium chloride the reduction of hydroxypyruvate is activated. Michaelis constants for these substrates of d-glycerate dehydrogenase and an equilibrium constant for the NAD-catalysed reaction have been calculated. 3. An explanation for the lowered V(max.) with d-glycerate as compared with dl-glycerate for the rabbit-kidney d-alpha-hydroxy acid dehydrogenase has been proposed.

THE METABOLISM OF VALERATE-3-C14 AND -5-C14 BY WHEAT STEM RUST UREDOSPORES

Uredospores of wheat stem rust took up about 90% of the carbon-14 present either as valerate-3-C14 or as valerate-5-C14 in M/30 phosphate buffer pH 6.2 in 3 hours. The initial valerate concentration was 0.017 mM and spores were supplied at the rate of 250 mg/30 ml of buffer. Carbon 3 of the valerate was largely respired as carbon dioxide but carbon 5 was extensively incorporated into spore components. Free amino acids contained about 40% of the radioactivity in the spores labelled with valerate-5-C14 and glutamic acid was highly labelled. Carbon 1 contained 8.1% and carbon 5, 3.8% of the carbon-14 in this glutamic acid and thus internal carbons contained 88%. The results with valerate-3-C14 and with valerate-5-C14 compare well with those of experiments done earlier with propionate-1-C14 and propionate-3-C14 respectively. It is concluded that propionate is formed from carbons 3, 4, and 5 of valerate, and thus that carbon 3 is converted to carbon dioxide, and carbons 4 and 5 to the carboxyl and methyl groups respectively of acetate.

PHYSIOLOGY OF THE SPORULATION PROCESS IN CLOSTRIDIUM BOTULINUM. I. CORRELATION OF MORPHOLOGICAL CHANGES WITH CATABOLIC ACTIVITIES, SYNTHESIS OF DIPICOLINIC ACID, AND DEVELOPMENT OF HEAT RESISTANCE

Day, Lawrence E. (Michigan State University, East Lansing), and Ralph N. Costilow. Physiology of the sporulation process in Clostridium botulinum. I. Correlation of morphological changes with catabolic activities, synthesis of dipicolinic acid, and development of heat resistance. J. Bacteriol. 88:690-694. 1964.-A reasonable degree of synchrony in the sporulation of Clostridium botulinum 62-A was attained by using a large inoculum of a young culture into a medium containing 4% Trypticase and 1 ppm of thiamine. Sporulation was complete within 24 to 36 hr. Cells harvested at various intervals were studied for their fermentative activity with l-alanine and l-proline as substrates. The Q values (microliters of gas per hour per milligram of dry cells) were maximal at the time a large percentage of the cells had initiated sporulation as indicated by swelling. They declined to a plateau at about the same level as found in vegetative cells by the time 10% of the cells had completed sporulation, and finally to a much lower level when sporulation was completed. The rates of accumulation of volatile acids (acetic, valeric, and propionic acids) corresponded closely with the catabolic potential observed. However, in the case of acetic acid, there was a significant decrease in the total acid present as the number of mature spores increased to over 50% of the final number. The total acetic acid then increased at a slow rate. The production of basic compounds during growth and sporulation more than balanced the rate of acid production, because the hydrogen ion concentration decreased exponentially throughout the period as indicated by the steady increase in pH. The synthesis of dipicolinic acid coincided closely with the development of heat resistance. Refractility developed 3 to 5 hr in advance of heat resistance.

ACCELERATION OF RENAL GLUCONEOGENESIS BY KETONE BODIES AND FATTY ACIDS

1. Acetoacetate or short-chain fatty acids (acetate, butyrate, propionate, n-hexanoate, n-octanoate) accelerate the rate of glucose formation from lactate, fumarate and other precursors in slices of kidney cortex (rat, rabbit, sheep). The cause of this acceleration has been investigated. 2. There are two different mechanisms of acceleration. At low concentrations of glucogenic precursors the acceleration is mainly due to a ;sparing' action. The substances which accelerate are oxidizable and serve as fuel of respiration in place of the glucogenic precursor. This is indicated by the fact that the ratio lactate used/glucose formed falls in the presence of the accelerators and approaches the value 2. 3. At high concentrations of lactate the acceleration appears to be mainly due to the activation of pyruvate carboxylase by acetyl-coenzyme A. The evidence in support of this is summarized. The results indicate that the activation of pyruvate carboxylase by acyl-coenzyme A discovered by Utter & Keech (1963) in purified enzyme preparations also occurs in crude tissue homogenates and can play a part in the control of oxaloacetate synthesis and gluconeogenesis.

CARBOHYDRATE METABOLISM IN LIVER FROM FOETAL AND NEONATAL SHEEP

1. During development of the sheep, the activities of UDP-glucose-alpha-glucan glucosyltransferase and UDP-glucose pyrophosphorylase and the glycogen content are highest in the liver of lambs 2 weeks old and considerably lower in liver from adult sheep. 2. The activity of hexokinase and the rate of incorporation of [(14)C]-glucose into glycogen are much lower in liver from postnatal sheep than in rat liver. 3. The activities of hexose diphosphatase and glucose 6-phosphatase and the rates of incorporation of [(14)C]pyruvate and [(14)C]propionate into glycogen increase from low levels in the liver of foetal sheep to maxima a few weeks after birth. The activities in the liver of adult sheep are slightly lower. 4. The incorporation rate of [(14)C]pyruvate into glucose has been measured in liver slices from rats, sheep and chick embryos at several ages of these animals. This pathway is active in liver from foetal sheep, embryonic chicks and postnatal rats or sheep, but is absent from the liver from foetal rats. 5. Fructose metabolism, as measured by the rates of incorporation of [(14)C]fructose into glycogen and glucose in liver slices and by assays of liver ketohexokinase, is barely detectable in the liver of foetal sheep and appears soon after birth. 6. During development of the sheep, the incorporation rate of [(14)C]galactose into glycogen in liver slices is highest in foetal sheep and decreases with increasing age of the animal. 7. These findings are discussed with reference to the changing pattern of carbohydrate metabolism during neonatal development of liver in the sheep.

PURIFICATION AND PROPERTIES OF ENZYMES INVOLVED IN THE PROPIONIC ACID FERMENTATION

Allen, S. H. G. (Western Reserve University, Cleveland, Ohio), R. W. Kellermeyer, R. L. Stjernholm, and Harland G. Wood. Purification and properties of enzymes involved in the propionic acid fermentation. J. Bacteriol. 87:171-187. 1964.-Chromatographic procedures are described for the separation and purification of phosphotransacetylase, acetyl kinase, malic dehydrogenase and coenzyme A (CoA) transferase. Purity of the enzymes was judged by homogeneity in an ultracentrifuge and by specific activity. Phosphotransacetylase was obtained 85% pure with a specific activity of 27.1. The preparation of acetyl kinase was a homogeneous protein with a specific activity of 531. The malic dehydrogenase likewise was homogeneous with a specific activity of 938. The CoA transferase, which was about 56% pure with a specific activity of 42.6, is the purest preparation of this enzyme yet described. The pH optimum was 6.5 to 7.8, and the K(m) for succinyl-CoA in the transfer of CoA to acetate was found to be 1.3 x 10(-4)m; for acetate, in the same transfer, the K(m) was 7.0 x 10(-3)m; for succinyl-CoA to propionate it was 6.8 x 10(-5)m, and for propionate, in the same reaction, 6.2 x 10(-4)m. Methods are described for the enzymatic production of methyl-malonyl-CoA, malonyl-CoA, propionyl-CoA, acetyl-CoA, and succinyl-CoA. The role of these enzymes in the propionic acid fermentation as well as the possible mechanism responsible for the high yields of adenosine triphosphate from glucose are considered.

THE MICROBIAL METABOLISM OF CINNAMIC ACID

A strain of Pseudomanas isolated from soil with cinnamic acid as a sole carbon source was found to be simultaneously adapted to the utilization of cinnamic acid and phenylpropionic acid. During growth on either of these compounds, o-hydroxyphenylpropionic acid and 2,3-dihydroxyphenylpropionic acid were produced in the culture medium. The organism, when grown on either cinnamic acid or phenylpropionic acid, was adapted to the utilization of m-hydroxyphenylpropionic acid and 2,3-dihydroxyphenylpropionic acid, but not to the utilization of o-hydroxyphenylpropionic acid. According to the principle of sequential induction introduced by Stanier, the initial steps in the metabolism of cinnamic acid appear to involve the intermediates phenylpropionic acid, m-hydroxyphenylpropionic acid, and 2,3-dihydroxyphenylpropionic acid.

CONVERSION OF GLUCOSE-C14 TO PROPIONATE BY THE RUMEN MICROBIOTA

Baldwin, R. L. (Michigan State University, East Lansing), W. A. Wood, and R. S. Emery. Conversion of glucose-C(14) to propionate by the rumen microbiota. J. Bacteriol 85:1346-1349. 1963.-Rumen microbiota enriched on three different diets calculated to present different levels of available carbohydrate were incubated with glucose-1-C(14), glucose-2-C(14), and glucose-6-C(14) to determine the contribution of the randomizing (succinate) and nonrandomizing (acrylate) routes to propionate. The propionate was labeled as though 70 to 100% was formed via the randomizing route and 0 to 30% via the nonrandomizing route. The contribution of the acrylate pathway increased with higher carbohydrate availability of the diet. These results are discussed with respect to earlier data using lactate-2-C(14) and lactate-3-C(14), and a unifying concept for both sets of data is presented.

METABOLISM OF PROPIONATE BY SHEEP LIVER. OXIDATION OF PROPIONATE BY HOMOGENATES

1. The rate and stability to aging of the metabolism of propionate by sheep-liver slices and sucrose homogenates were examined. Aging for up to 20min. at 37 degrees in the absence of added substrate had little effect with slices, whole homogenates or homogenates without the nuclear fraction. 2. Metabolism of propionate by sucrose homogenates was confined to the mitochondrial fraction, but the mitochondrial supernatant (microsomes plus cell sap) stimulated propionate removal. 3. The rate of propionate metabolism by liver slices was higher in a high potassium phosphate-bicarbonate medium [0.88(+/-s.e.m. 0.16)mumole/mg. of N/hr.] than in Krebs-Ringer bicarbonate medium [0.44(+/-s.e.m. 0.13)mumole/mg. of N/hr.]. 4. Metabolism of propionate by sucrose homogenates freed from nuclei was dependent on the presence of oxygen, carbon dioxide and ATP. Propionate removal was stimulated 250% by Mg(2+) ions and 670% by cytochrome c. 5. In the complete medium 2.39(+/-s.e.m. 0.15)mumoles of propionate were consumed/mg. of N/hr. 6. The ratio of oxygen consumption to propionate utilization was sufficient to account for the complete oxidation of half the propionate consumed. 7. The only products detected under these conditions were succinate, fumarate and malate. Propionate had no effect on the production of lactate from endogenous sources and did not itself give rise to lactate. 8. Methylmalonate did not accumulate when propionate was metabolized and was not oxidized. It was detected as an intermediate in the conversion of propionyl-CoA into succinate. The rate of this reaction sequence was adequate to account for the rate of propionate metabolism by sucrose homogenates or slices, provided that the rate of formation of propionyl-CoA was not limiting. 9. The methylmalonate pathway was predominantly a mitochondrial function. 10. The metabolism of propionate appeared to be dependent on active oxidative phosphorylation.

MICROBIAL GROWTH ON C1 COMPOUNDS. SYNTHESIS OF CELL CONSTITUENTS BY METHANE- AND METHANOL-GROWN PSEUDOMONAS METHANICA

1. A study has been made of the incorporation of carbon from [(14)C]methane, [(14)C]methanol and [(14)C]bicarbonate by cultures of Pseudomonas methanica growing on methane, and [(14)C]methanol by cultures of the same organism growing on methanol. 2. The distribution of radioactivity within the non-volatile constituents of the ethanol-soluble fractions of the cells, after incubation with labelled compound for periods up to 3min., has been analysed by chromatography and radioautography. 3. Over 90% of the radioactivity fixed from [(14)C]methane or [(14)C]methanol at the earliest times of sampling appeared in phosphorylated compounds. Glucose phosphate and fructose phosphate together constituted the largest part of the radioactive phosphates (70-90%); phosphoglycerate was a relatively minor component (2-17%). Other compounds becoming labelled during the incubation included glycine, serine, glutamate, aspartate, malate, citrate and alanine. 4. The first stable products of [(14)C]bicarbonate fixation were malate and aspartate (containing between them over 90% of the total radioactivity fixed at the earliest times of sampling). 5. The percentage of the total radioactivity fixed that was contained in each of the radioactive compounds has been plotted against time. The slopes of the curves obtained show that hexose phosphates are primary stable products of [(14)C]methane and [(14)C]methanol incorporation and that aspartate and malate are primary stable products of [(14)C]bicarbonate incorporation. 6. No carboxydismutase activity has been found in cell-free extracts of the organism. This fact, together with the other findings, shows that an autotrophic metabolism involving the ribulose diphosphate cycle of carbon dioxide fixation cannot be operating.