METHYLMALONYL ISOMERASE, II. PURIFICATION AND PROPERTIES OF THE ENZYME FROM PROPIONIBACTERIA

THE GENUS VEILLONELLA . II. NUTRITIONAL STUDIES

Rogosa, M. (National Institute of Dental Research, U.S. Public Health Service, Bethesda, Md.), and Ferial S. Bishop. The genus Veillonella. II. Nutritional studies. J. Bacteriol. 87:574-580. 1964.-A medium is described for the study of the vitamin, hypoxanthine, putrescine, or cadaverine requirements of 86 Veillonella isolates from man, rabbit, rat, and hamster. No organism required riboflavine or folic acid for growth. Niacin and calcium pantothenate were often stimulatory, but in nearly all cases were dispensable. Biotin and p-aminobenzoic acid were frequently stimulatory and sometimes indispensable for continued growth. V. parvula (antigenic group VI) required pyridoxal and thiamine and did not require putrescine or cadaverine. V. alcalescens (antigenic group IV) required pyridoxal, generally required thiamine, and also required putrescine or cadaverine. Of the isolates, 25 from the rat and 3 from the hamster (antigenic group II) generally behaved like V. parvula, except that a putrescine or cadaverine requirement was often observed. Spermine, spermidine, and agmatine could not replace putrescine or cadaverine. Although succinate is metabolized by resting cells, the organisms could not grow with succinate as an energy source.

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.

Fermentative degradation of glutarate via decarboxylation by newly isolated strictly anaerobic bacteria

Two strains of new strictly anaerobic, gram-negative bacteria were enriched and isolated from a freshwater (strain WoG13) and a saltwater (strain CuG11) anoxic sediment with glutarate as sole energy source. Strain WoG13 formed spores whereas strain CuG11 did not. Both strains were rod-shaped, motile bacteria growing in carbonate-buffered, sulfide-reduced mineral medium supplemented with 2% of rumen fluid. Both strains fermented glutarate to butyrate, isobutyrate, CO2, and small amounts of acetate. With methylsuccinate, the same products were formed, and succinate was fermented to propionate and CO2. No sugars, amino acids or other organic acids were used as substrates. Molar growth yields (Ys) were very small (0.5-0.9 g cell dry mass/mol dicarboxylate). Cells of strain WoG13 contained no cytochromes, and the DNA base ratio was 49.0 +/- 1.4 mol% guanine-plus-cytosine. Enzyme activities involved in glutarate degradation could be demonstrated in cell-free extracts of strain WoG13. A pathway of glutarate fermentation via decarboxylation of glutaconyl-CoA to crotonyl-CoA is suggested which forms butyrate and partly isobutyrate by subsequent isomerization.

Two pathways of glutamate fermentation by anaerobic bacteria

Two pathways are involved in the fermentation of glutamate to acetate, butyrate, carbon dioxide, and ammonia-the methylaspartate and the hydroxyglutarate pathways which are used by Clostridium tetanomorphum and Peptococcus aerogenes, respectively. Although these pathways give rise to the same products, they are easily distinguished by different labeling patterns of the butyrate when [4-(14)C]glutamate is used as substrate. Schmidt degradation of the radioactive butyrate from C. tetanomorphum yielded equally labeled propionate and carbon dioxide, whereas nearly all the radioactivity of the butyrate from P. aerogenes was recovered in the corresponding propionate. This procedure was used as a test for the pathway of glutamate fermentation by 15 strains (9 species) of anaerobic bacteria. The labeling patterns of the butyrate indicate that glutamate is fermented via the methylaspartate pathway by C. tetani, C. cochlearium, and C. saccarobutyricum, and via the hydroxyglutarate pathway by Acidaminococcus fermentans, C. microsporum, Fusobacterium nucleatum, and F. fusiformis. Enzymes specific for each pathway were assayed in crude extracts of the above organisms. 3-Methylaspartase was found only in clostridia which use the methylaspartate pathway, including Clostridium SB4 and C. sticklandii, which probably degrade glutamate to acetate and carbon dioxide by using a second amino acid as hydrogen acceptor. High levels of 2-hydroxyglutarate dehydrogenase were found exclusively in organisms that use the hydroxyglutarate pathway. The data indicate that only two pathways are involved in the fermentation of glutamate by the bacteria analyzed. The methylaspartate pathway appears to be used only by species of Clostridium, whereas the hydroxyglutarate pathway is used by representatives of several genera.

On the mechanism of action of vitamin B 12 . Model studies. Thermal rearrangement of methyl 3,3-dimethylglycidate to methyl levulinate

The discovery that methyl 3,3-dimethylglycidate rearranges to methyl levulinate on heating is discussed in terms of its possible consequences for the mechanism of action of the coenzyme B(12)-dependent enzymes: methylmalonyl-CoA mutase (EC 5.4.99.2), glutamate mutase (EC 5.4.99.1), and a-methyleneglutarate mutase. It is also suggested that the proposed mechanism may provide a unifying link between the mechanism of action of the above enzymes and that of the coenzyme B(12)-dependent dioldehydrase and related enzymes.

Methylmalonate Excretion in Vitamin B12 Deficiency

Urinary methylmalonate excretion is increased in rats with an insufficiency of vitamin B(12). Excretion of methylmalonate is not affected by folic acid, vitamin E, or selenium, but is markedly decreased by small amounts of vitamin B(12) added to the diet.

THE INFLUENCE OF COBAMIDES ON THE ENDOGENOUS AND EXOGENOUS RESPIRATION OF A MARINE BACTERIUM

The oxidation of propionate, isobutyrate, valerate, isoleucine, and valine as well as the endogenous respiration of a B12-dencient marine bacterium was stimulated by the addition of vitamin B12to washed cell suspensions. The B12analog, 2-methyladenylcobamide cyanide, also stimulated endogenous respiration, but cobinamide was inactive. During autorespiration ammonia was continuously evolved by the cells indicating the presence of a nitrogenous endogenous substrate. When vitamin B12was supplied to the cells, the ammonia evolved was decreased, while the rate of oxygen uptake was increased. The possible involvement of cobamide coenzymes is discussed in relation to these findings.

FACTORS INVOLVED IN THE BACTERIAL DECARBOXYLATION OF SUCCINIC ACID

The succinic decarboxylase system of Veillonella alcalescens loses activity when aged at 2 °C for a few days. Evolution of CO2 by aged extracts of this organism was greatly stimulated by boiled cell-free extracts of Propionibacterium pentosaceum. These boiled extracts could not be replaced by coenzyme A (CoA), adenosine triphosphate (ATP), magnesium ions, biotin, or dimethylbenzimidazolylcobamide coenzyme (DBC).