L-serine specific dehydrase from Clostridium acidi-urici

Acetate formation in Clostridium acidi-urici: acetokinase

Sagers, Richard D. (University of Illinois, Urbana), Moshe Benziman, and I. C. Gunsalus. Acetate formation in Clostridium acidiurici: Acetokinase. J. Bacteriol. 82:233-238. 1961.-To define the energy-yielding reaction(s) during fermentation of purines by Clostridium acidi-urici, an eightfold purified acetokinase was obtained by protamine and ammonium sulfate fractionation of crude extracts. Enzyme activity was determined by measuring the disappearance of acetyl phosphate using adenosine diphosphate (ADP) as phosphate acceptor or by following the generation of acetyl phosphate from adenosine triphosphate (ATP) + acetate. The optimal pH for the reaction was observed to be 7.4. K(m) values for acetyl phosphate, ADP, and magnesium ions were shown to be 2.1 x 10(-3)m, 3.2 x 10(-3)m, and 2.4 x 10(-3)m, respectively. Acetyl phosphate disappearance is dependent upon ADP and is stoichiometric with addition of the latter. The acetokinase reaction probably represents the major energy-yielding reaction during purine fermentation by this organism. A pathway for acetate generation from formiminoglycine is proposed, and evidence for a number of enzyme activities intermediate between formiminoglycine degradation and acetate formation is given. The enzyme activities demonstrated are compatible with the over-all purine fermentation rate by whole cells.

FAILURE OF ARSENATE TO UNCOUPLE THE PHOSPHOTRANSACETYLASE SYSTEM IN CLOSTRIDIUM ACIDIURICI

Sagers, Richard D. (Brigham Young University, Provo, Utah), Moshe Benziman, and Sigrid M. Klein. Failure of arsenate to uncouple the phosphotransacetylase system in Clostridium acidiurici. J. Bacteriol. 86:978-984. 1963.-The conversion of pyruvate to acetyl phosphate by extracts of Clostridium acidiurici required coenzyme A (CoA), an electron-carrier system (ferredoxin and nicotinamide adenine dinucleotide), and a divalent metal. Other cofactors may be involved but are not presently defined. The metal activates the system transferring acetyl units between CoA and phosphate. Acetyl CoA could be generated from pyruvate or from acetyl phosphate, but in both cases arsenate failed to uncouple the high-energy acyl compounds. The rate of acetyl transfer between acetyl phosphate and CoA was markedly decreased by 0.005 m arsenate, but the generation of acetyl CoA from pyruvate was essentially unaffected until the arsenate concentration exceeded 0.02 m. Close agreement was observed between the amount of pyruvate utilized and the amount of acetyl phosphate formed, both in the presence and absence of arsenate. The CoA-dependent exchange of P(32)O(4) ( identical with) with acetyl phosphate proceeded at a rate approximately one-eightieth of the rate of acetylation of CoA, indicating an equilibrium value for the phosphotransacetylase reaction similar to that observed for Clostridium kluyveri. The failure of arsenate to uncouple the C. acidiurici enzyme may indicate a high degree of specificity in relation to the acetyl unit acceptor, giving preference to phosphate over arsenate.

Family Spirosomaceae: gram-negative ring-forming aerobic bacteria

The bacteria having a unique ring-like morphology first isolated from nasal mucus by Weibel in 1887 were classified as a new genus Spirosoma by Migula in 1894. However, because these bacteria were not completely described for taxonomic purposes and their cultures were no longer available, the genus was deleted from the Bergey's Manual of Determinative Bacteriology, 6th edition, 1948. Orskov (1928) created a new genus "Microcyclus" (a name that has been found to be illegitimate and replaced with Ancylobacter by Raj 1983) to describe these nonmotile vibroid bacteria that occasionally formed ring-like structures. Several similar isolates found in many countries during the last 60 years were readily identified with this genus on the basis of the characteristic morphology alone. For the first time, these fascinating bacteria were extensively reviewed by Raj in 1977 and again in 1981. However, during the last decade, the systematics of these microcyclus bacteria has been reexamined and redefined. It has been shown that these Gram-negative ring-forming aerobic bacteria constitute a heterogeneous group of five genera: Ancylobacter, Cyclobacterium, Flectobacillus, Runella, and Spirosoma; the last four genera have been grouped into a family Spirosomaceace (reviving the old discarded name originally proposed by Migula 1894), thus separating them from the genus Ancylobacter which remains unaffiliated with any family yet (Bergey's Manual of Systematic Bacteriology, Vol. I, 9th ed., 1984). Also, this article reviews the recent studies reported on the ecology, morphogenesis, metabolism, and physiology of the picturesque bacteria.

Serine utilization by Klebsiella aerogenes

Klebsiella aerogenes was found to contain a specific L-serine dehydrase that was induced by threonine, glycine or leucine, but not by its substrate. Cellular concentrations were sensitive to carbon rather than nitrogen sources in the growth medium. A nonspecific isoleucine-sensitive L-threonine dehydrase supplemented the specific L-serine dehydrase activity. K. aerogenes also contains a leucine-inducible L-threonine dehydrogenase which probably initiated a threonine-utilization pathway in which the serine-specific dehydrate participated. Strains that were altered in their ability to metabolize serine differed in either L-serine dehydrase or L-threonine dehydrase activity. Thus, K. aerogenes growing on L-serine as a sole nitrogen source relies upon two enzymes that metabolize the amino acid as subsidiary functions.

Studies on L-serine deaminase in Escherichia coli K-12

l-Serine deaminase has been studied in toluene-treated cells of Escherichia coli K-12 and shown to be a discrete entity distinct from l-threonine deaminase. Its level in the cell varies as a function of nitrogen nutrition, carbon source, and amino acids (glycine and leucine). The metabolic role of the enzyme remains unclear but may be related to serine toxicity. The enzyme is unstable within the cell in the presence of its inducers, glycine and leucine, but not in their absence.

Ferrous ion-dependent L-serine dehydratase from Clostridium acidiurici

l-Serine dehydratase from Clostridium acidiurici was purified 400-fold. The enzyme required activation by catalytic amounts of ferrous ion and a thiol reducing agent before the addition of substrate. Several cations tested were unable to substitute for divalent iron. The reducing agent of choice was dithiothreitol. The activation was presumed to result in the formation of an iron-enzyme complex, because once activated the enzyme retained essentially full activity in a reaction mixture not supplemented with iron or reducing agent. The reaction with substrate was carried out at pH 8.4 in phosphate buffer and was specific for l-serine. The presence of pyridoxal phosphate as coenzyme was indicated by absorption maxima at 330 and 420 nm and fluorescence maxima at 390 and 520 nm.

L-serine deaminase of Escherichia coli

The native l-serine deaminase (l-serine hydrolyase, deaminating, EC 4.2.1.13) of Escherichia coli K-12, which seems to be a very labile protein, is rather stable in concentrated solution. Dilution rapidly inactivates it, but in the presence of a saturating concentration of l-serine the molecule is protected from inactivation. It is a very specific enzyme; l-serine is the sole substrate with a K(m) value of 6.60 x 10(-3)m. d-Serine and l-cysteine are competitive inhibitors. Substrate saturation curves of the native enzyme show sigmoid shape, whereas the enzyme liberated from the bacteria in the presence of l-serine exhibits normal Michaelis-Menten kinetics.

L-serine dehydratase (deaminase) of psychrophiles and mesophiles from polar and temperate habitats

Escherichia coli and Pseudomonas aeruginosa were grown at several temperatures ranging from 0° to 37 °C and assayed at each temperature for L-serine dehydratase activity. The relationship between enzymatic activity and growth temperature is quite different for the mesophile and psychrophile. In addition, the stimulatory effect of natural plant lecithin upon serine deamination was different for each organism, suggesting that there is either a difference in permeability or that this substance has a more direct role in enzymic activity. Also included are data confirming the results of other workers.

Radiorespirometric studies of Leucothrix mucor

Catabolic capabilities of Leucothrix mucor were studied by radiorespirometric technique with a liquid scintillation spectrometer. Through measurement of relative rates and total percentages of (14)CO(2) produced, together with the determination of the cellular incorporation of (14)C from different carbon atoms of various labeled substrates, such as simple carbohydrates, intermediary metabolites, and amino acids, the essential characteristics of the primary and secondary pathways operative in this organism were examined. These substrates appeared to be degraded mainly via enzymes of the Entner-Doudoroff pathway in conjunction with the tricarboxylic acid cycle. Estimation of concurrent participation of pathways indicated that 20 to 25% of the administered carbohydrate was catabolized via the pentose phosphate pathway. There was no evidence of the Embden-Meyerhof-Parnas pathway operating in this organism.

Acetate formation in Clostridium acidi-urici: acetokinase

Sagers, Richard D. (University of Illinois, Urbana), Moshe Benziman, and I. C. Gunsalus. Acetate formation in Clostridium acidiurici: Acetokinase. J. Bacteriol. 82:233-238. 1961.-To define the energy-yielding reaction(s) during fermentation of purines by Clostridium acidi-urici, an eightfold purified acetokinase was obtained by protamine and ammonium sulfate fractionation of crude extracts. Enzyme activity was determined by measuring the disappearance of acetyl phosphate using adenosine diphosphate (ADP) as phosphate acceptor or by following the generation of acetyl phosphate from adenosine triphosphate (ATP) + acetate. The optimal pH for the reaction was observed to be 7.4. K(m) values for acetyl phosphate, ADP, and magnesium ions were shown to be 2.1 x 10(-3)m, 3.2 x 10(-3)m, and 2.4 x 10(-3)m, respectively. Acetyl phosphate disappearance is dependent upon ADP and is stoichiometric with addition of the latter. The acetokinase reaction probably represents the major energy-yielding reaction during purine fermentation by this organism. A pathway for acetate generation from formiminoglycine is proposed, and evidence for a number of enzyme activities intermediate between formiminoglycine degradation and acetate formation is given. The enzyme activities demonstrated are compatible with the over-all purine fermentation rate by whole cells.