Quantification Of Glucose Metabolism Research Articles

Quantification of Glucose Metabolism and Nitrogen Utilization in Two Brassicaceae Species under Bicarbonate and Variable Ammonium Soil Conditions.

In karst habitats under drought conditions, high bicarbonate (high pH), and an abundant nitrate soil environment, bicarbonate regulates the glycolysis (EMP) and pentose phosphate pathways (PPP), which distribute ATP and NADPH, affecting nitrate (NO3-) and ammonium (NH4+) utilization in plants. However, the relationship between EMP PPP and NO3-, and NH4+ utilization and their responses to bicarbonate and variable ammonium still remains elusive. In this study, we used Brassica napus (Bn, a non-karst-adaptable plant) and Orychophragmus violaceus (Ov, a karst-adaptable plant) as plant materials, employed a bidirectional nitrogen-isotope-tracing method, and performed the quantification of the contribution of EMP and PPP. We found that bicarbonate and ammonium inhibited glucose metabolism and nitrogen utilization in Bn under simulated karst habitats. On the other hand, it resulted in a shift from EMP to PPP to promote ammonium utilization in Ov under high ammonium stress in karst habitats. Compared with Bn, bicarbonate promoted glucose metabolism and nitrogen utilization in Ov at low ammonium levels, leading to an increase in photosynthesis, the PPP, carbon and nitrogen metabolizing enzyme activities, nitrate/ammonium utilization, and total inorganic nitrogen assimilation capacity. Moreover, bicarbonate significantly reduced the growth inhibition of Ov by high ammonium, resulting in an improved PPP, RCRUBP, and ammonium utilization to maintain growth. Quantifying the relationships between EMP, PPP, NO3-, and NH4+ utilization can aid the accurate analysis of carbon and nitrogen use efficiency changes in plant species. Therefore, it provides a new prospect to optimize the nitrate/ammonium utilization in plants and further reveals the differential responses of inorganic carbon and nitrogen (C-N) metabolism to bicarbonate and variable ammonium in karst habitats.

Experimental Identification and Quantification of Glucose Metabolism in Seven Bacterial Species

The structurally conserved and ubiquitous pathways of central carbon metabolism provide building blocks and cofactors for the biosynthesis of cellular macromolecules. The relative uses of pathways and reactions, however, vary widely among species and depend upon conditions, and some are not used at all. Here we identify the network topology of glucose metabolism and its in vivo operation by quantification of intracellular carbon fluxes from 13C tracer experiments. Specifically, we investigated Agrobacterium tumefaciens, two pseudomonads, Sinorhizobium meliloti, Rhodobacter sphaeroides, Zymomonas mobilis, and Paracoccus versutus, which grow on glucose as the sole carbon source, represent fundamentally different metabolic lifestyles (aerobic, anaerobic, photoheterotrophic, and chemoheterotrophic), and are phylogenetically distinct (firmicutes, gamma-proteobacteria, and alpha-proteobacteria). Compared to those of the model bacteria Escherichia coli and Bacillus subtilis, metabolisms of the investigated species differed significantly in several respects: (i) the Entner-Doudoroff pathway was the almost exclusive catabolic route; (ii) the pentose phosphate pathway exhibited exclusively biosynthetic functions, in many cases also requiring flux through the nonoxidative branch; (iii) all aerobes exhibited fully respiratory metabolism without significant overflow metabolism; and (iv) all aerobes used the pyruvate bypass of the malate dehydrogenase reaction to a significant extent. Exclusively, Pseudomonas fluorescens converted most glucose extracellularly to gluconate and 2-ketogluconate. Overall, the results suggest that metabolic data from model species with extensive industrial and laboratory history are not representative of microbial metabolism, at least not quantitatively.