Partial purification and some properties of a latent CO2 reductase from green potato tuber chloroplasts

Ti3C2 MXene/MoS2@AuNPs ternary nanocomposite for highly sensitive electrochemical detection of phoxim residues in fruits

Phoxim, extensively utilized in agriculture as an organothiophosphate insecticide, has the potential to cause neurotoxicity and pose human health hazards. In this study, an electrochemical enzyme biosensor based on Ti3C2 MXene/MoS2@AuNPs/AChE was constructed for the sensitive detection of phoxim. The two-dimensional multilayer structure of Ti3C2 MXene provides a robust framework for MoS2, leading to an expansion of the specific surface area and effectively preventing re-stacking of Ti3C2 MXene. Additionally, the synergistic effect of self-reduced grown AuNPs with MoS2 further improves the electrical conductivity of the composites, while the robust framework provides a favorable microenvironment for immobilization of enzyme molecules. Ti3C2 MXene/MoS2@AuNPs electrochemical enzyme sensor showed a significant response to phoxim in the range of 1 × 10-13 M to 1 × 10-7 M with a detection limit of 5.29 × 10-15 M. Moreover, the sensor demonstrated excellent repeatability, reproducibility, and stability, thereby showing its promising potential for real sample detection.

Formaldehyde assimilation through coordination of the glyoxylate pathway and the tricarboxylic acid cycle in broad bean roots

Formaldehyde (HCHO) assimilation in broad bean (Vicia faba L. cv. YD) roots was investigated using ¹³C-labeled HCHO followed by ¹³C-NMR analysis. Results revealed that H¹³CHO was first oxidized to H¹³COOH in the roots treated with 2 mM H¹³CHO in a time-dependent manner. Subsequently, a massive signal peak of [2, 4-¹³C]citrate (Cit) and a signal peak of [2, 3-¹³C]succinate (Su) were observed in accompany with an enhancement in the signal intensity of [3-¹³C]Cit. The data suggested that the glyoxylate pathway and the tricarboxylic acid (TCA) cycle functioned simultaneously in the subsequent assimilation of H¹³COOH. The yield of [2, 4-¹³C]Cit accounted for more than 80% of the total metabolites. The activity of isocitrate lyase (ICL), a key enzyme in the glyoxylate pathway, was stimulated by HCHO in a dosage-dependent manner. As a result, [2, 4-¹³C]Cit production was increased significantly in YD roots treated with high concentrations (4 and 6 mM) of H¹³CHO. Moreover, induction of the ICL activity by methanol resulted in a simultaneous elevation in the production of [2, 4-¹³C]Cit and [3-¹³C]Cit in methanol-pretreated roots under 2 mM H¹³CHO stress. Pretreatment of roots with cyclosporin A, which hinders the transport of ¹³C-enriched compounds into mitochondria, caused a notable decline in the signal peak and yield of [2, 4-¹³C]Cit and consequently induced a notable accumulation of [2, 3-¹³C]Su and an increase in the HCO₃^- production (generated from H¹³COOH oxidation) in H¹³CHO-treated roots. These results suggested that the glyoxylate pathway and the TCA cycle function coordinately in HCHO assimilation in broad bean roots.

ONE-CARBON METABOLISM IN HIGHER PLANTS

The metabolism of one-carbon (C1) units is essential to plants, and plant C1 metabolism has novel features not found in other organisms-plus some enigmas. Despite its centrality, uniqueness, and mystery, plant C1 biochemistry has historically been quite poorly explored, in part because its enzymes and intermediates tend to be labile and low in abundance. Fortunately, the integration of molecular and genetic approaches with biochemical ones is now driving rapid advances in knowledge of plant C1 enzymes and genes. An overview of these advances is presented. There has also been progress in measuring C1 metabolite fluxes and pool sizes, although this remains challenging and there are relatively few data. In the future, combining reverse genetics with flux and pool size determinations should lead to quantitative understanding of how plant C1 pathways function. This is a prerequisite for their rational engineering.

Plant one-carbon metabolism and its engineering

The metabolism of one-carbon (C1) units is vital to plants. It involves unique enzymes and takes place in four subcellular compartments. Plant C1 biochemistry has remained relatively unexplored, partly because of the low abundance or the lability of many of its enzymes and intermediates. Fortunately, DNA sequence databases now make it easier to characterize known C1 enzymes and to discover new ones, to identify pathways that might carry high C1 fluxes, and to use engineering to redirect C1 fluxes and to understand their control better.

Purification and characterization of glyoxylate synthetase from greening potato-tuber chloroplasts

Glyoxylate synthetase catalyzing the condensation of two formate molecules into glyoxylate was purified to homogeneity by AcA-34, Sepharose CL-6B and DEAE-Sepharose CL-6B chromatography. A 150-fold purification with a specific activity of 25 mumol . mg protein-1 x 5 min-1 was obtained by this procedure. The reaction product was identified as glyoxylate. The enzyme was a tetramer having a molecular mass of 160 kDa with a subunit molecular mass of 40 kDa. The enzyme could be activated 3-4-fold by the addition of 0.3 mM Fe2+ and 0.4 mM tetrahydrofolic acid to the reaction mixture. The requirement for Fe2+ and tetrahydrofolic acid was confirmed from the inhibition of enzyme by O-phenanthroline and alpha-aminopterin, respectively. The presence of a bound folate in the enzyme was indicated by the fluorescence emission at 450 nm and turbidity development in a Lactobacillus casei growth test. Fluorescence emission at 450 nm upon excitation at 280 nm indicated that the bound folate and the aromatic amino-acid residues of the enzyme were in close vicinity. The enzyme was maximally active at 25 degrees C and exhibited a pH optimum at 7.0. The concentration of substrate was optimal at 5.0 mM and Km for substrate was found to be 1.4 mM. Activation by Fe2+ did not alter the Km but caused an increase in Vmax. The enzyme contained about 14-16 disulfide linkages, of which two were found to be reduced by treatment with 2-mercaptoethanol. The presence of excess 2-mercaptoethanol in the enzyme was inhibitory, indicating that the two disulfide linkages reduced by 2-mercaptoethanol were essential for activity. This was also confirmed by the inhibition of enzyme activity when reduced enzyme was treated with O-phthalaldehyde, which formed a thioisoindole derivative with reduced thiol groups at the active site.