Studies on two isozymes of aconitase from Bacillus cereus T. III. Enzymatic properties

The tricarboxylic acid cycle in L₃ Teladorsagia circumcincta: metabolism of acetyl CoA to succinyl CoA

Nematodes, like other species, derive much of the energy for cellular processes from mitochondrial pathways including the TCA cycle. Previously, we have shown L₃ Teladorsagia circumcincta consume oxygen and so may utilise a full TCA cycle for aerobic energy metabolism. We have assessed the relative activity levels and substrate affinities of citrate synthase, aconitase, isocitrate dehydrogenase (both NAD+ and NADP+ specific) and α-ketoglutarate dehydrogenase in homogenates of L₃ T. circumcincta. All of these enzymes were present in homogenates. Compared with citrate synthase, low levels of enzyme activity and low catalytic efficiency was observed for NAD+ isocitrate dehydrogenase and especially α-ketoglutarate dehydrogenase. Therefore, it is likely that the activity of these to enzymes regulate overall metabolite flow through the TCA cycle, especially when [NAD+] limits enzyme activity. Of the enzymes tested, only citrate synthase had substrate affinities which were markedly different from values obtained from mammalian species. Overall, the results are consistent with the suggestion that a full TCA cycle exists withinL₃ T. circumcincta. While there may subtle variations in enzyme properties, particularly for citrate synthase, the control points for the TCA cycle inL₃ T. circumcincta are probably similar to those in the tissues of their host species.

Long-term prediction of fish growth under varying ambient temperature using a multiscale dynamic model

Background

Feed composition has a large impact on the growth of animals, particularly marine fish. We have developed a quantitative dynamic model that can predict the growth and body composition of marine fish for a given feed composition over a timespan of several months. The model takes into consideration the effects of environmental factors, particularly temperature, on growth, and it incorporates detailed kinetics describing the main metabolic processes (protein, lipid, and central metabolism) known to play major roles in growth and body composition.

Results

For validation, we compared our model's predictions with the results of several experimental studies. We showed that the model gives reliable predictions of growth, nutrient utilization (including amino acid retention), and body composition over a timespan of several months, longer than most of the previously developed predictive models.

Conclusion

We demonstrate that, despite the difficulties involved, multiscale models in biology can yield reasonable and useful results. The model predictions are reliable over several timescales and in the presence of strong temperature fluctuations, which are crucial factors for modeling marine organism growth. The model provides important improvements over existing models.

Purification of aconitase from Bacillus subtilis and correlation of its N-terminal amino acid sequence with the sequence of the citB gene

The DNA sequence for the promoter region of the Bacillus subtilis citB gene has been determined. Presumed "-10" and "-35" regions of the promoter have been identified, and transcriptional and translational start points of citB have been located. To correlate the DNA sequence of citB with the amino acid sequence of its presumed product, aconitase, it was necessary to devise a scheme for purification of this labile enzyme. This procedure relies on the ability to restore enzyme activity at each stage of purification by incubation in a reducing buffer containing a source of ferrous ions. B. subtilis aconitase appears to be a monomer with a molecular weight of approximately 120,000. The amino-terminal amino acids of aconitase fit the sequence predicted by analysis of the citB gene. Thus, citB codes for aconitase.