Untersuchungen zum Glyoxyls�urestoffwechsel vonBacillus fastidiosus Stamm 83

Evolutionary Aspects of the Oxido-Reductive Network of Methylglyoxal

In the chemoautotrophic theory for the origin of life, offered as an alternative to broth theory, the archaic reductive citric acid cycle operating without enzymes is in the center. The non-enzymatic (methyl)glyoxalase pathway has been suggested to be the anaplerotic route for the reductive citric acid cycle. In the recent years, much has been learned about methylglyoxal, but its importance in the metabolic machinery is still uncovered. If methylglyoxal had been essential participant of the early stage of evolution, then it is a legitimate question whether it might have played a role in the early oxido-reduction network, too. Therefore, an oxido-reduction network of methylglyoxal that might have functioned under ancient circumstances without enzymes was constructed and analyzed by virtue of group contribution method. Taking methylglyoxal as input material, it turned out that the evolutionary value of reactions and biomolecules were not similar. Glycerol, glycerate, and tartonate, the output components, were conserved to different degrees. Although the tartonate route was similarly favorable from energetic point of view, its intermediates are almost not present in extant biochemistry. The presence of two carboxyl or aldehyde groups, or their combination in tricarbons of the constructed network seemed disadvantageous for selection, and the inductive effect, resulting in an asymmetry in electron cloud of chemicals, might have been important. The evolutionary role for cysteine, H₂S, and formaldehyde in the emergence of high-energy bonds in the form of thioesters and in Fe-S cluster formation as well as in imidazole synthesis was shown to bridge the gap between prebiotic chemistry and contemporary biochemistry. Overall, the ideas developed here represent an approach fitting to chemoautotrophic origin of life and implying to the role of methylglyoxal in triose formation. The proposed network is expected to have an impact upon how one may think of prebiological chemical processes on methylglyoxal, too. Finally, along the evolutionary time line, the network functioning without enzymes is situated between the formation of simple organic compounds and primeval cells, being closer to the former and well preceding the last common metabolic ancestor developed after primitive cells emerged.

The level of enzymes involved in the allantoin metabolism of Bacillus fastidiosus grown under different conditions

Bacillus fastidiosus was cultivated in batch and continuous culture on various carbon and nitrogen sources. The enzymes involved in allantoin degradation (allantoinase, urease, carboligase) of B. fastidiosus were hardly affected by either carbon or nitrogen source. In contrast, the enzymes involved in glycerol utilization (glycerol kinase, glycerol 3-phosphate dehydrogenase) were induced during growth on glycerol, but were not affected by the amount of allantoin present.

Purification and characterization of the NADP-dependent glutamate dehydrogenase from Bacillus fastidiosus

Ammonia assimilation in Bacillus fastidiosus proceeds via the NADP-dependent glutamate dehydrogenase. The enzyme, purified to homogeneity, is composed of identical subunits with a molecular weight of about 48,000 dalton. Presumably the enzyme is a hexamer. The enzyme is specific for NADP(H). The pH optima for the amination and deamination reactions are 7.7 and 8.6, respectively. The temperature optimum is 60 degrees C. Furthermore, temperature stability and apparent Km values for substrates of both the amination and deamination reactions were determined. Several metabolites were tested for their effect on the enzyme activity. Only malate and fumarate showed some inhibitory effect.

Stimulation of growth of Bacillus fastidiosus by amino acids

Growth of Bacillus fastidiosus on allantoin is stimulated by components of rich media as was evident from a decreased generation time and an increased maximal growth yield in the presence of such media. Such a stimulation must involve various transport systems. Energy-dependent transport systems for some amino acids were demonstrated besides those for urate, allantoin and allantoate.

Purification and some properties of hydroxypyruvate isomerase of Bacillus fastidiosus

Hydroxypyruvate isomerase of Bacillus fastidiosus is a novel enzyme (Braun, W. and Kaltwasser, H. (1979) Arch. Microbiol. 121, 129-134) which catalyzes the reversible conversion of tartronate semialdehyde into hydroxypyruvate. The enzyme was purified to homogeneity. The native molecule had a molecular weight of 265 000-280 000 and was composed of six subunits with a molecular weight of 45 000. The enzyme showed optimal activity at pH 6.6-7.4 and 57 degrees C. Hydroxypyruvate isomerase is stable on heating for 10 min at 67 degrees C. The enzyme appeared to be specific for tartronate semialdehyde and hydroxypyyruvate and no cofactors were involved in the reaction. The equilibrium constant K = [tartronate semialdehyde] divided by [hydroxypyruvate] was found to be 2.5 at pH 7.1, and 30 degrees C.