China
Africa
Explore chapters and articles related to this topic
Fuel Metabolism in the Fetus
Published in Emilio Herrera, Robert H. Knopp, Perinatal Biochemistry, 2020
In the adult liver when large amounts of glucose are present in the portal vein, glucose is transported into the hepatocyte by a specific glucose transporter (GLUT-2)3 which is a low-affinity, high-capacity, transport system (facilitated diffusion). It is then phosphorylated by glucokinase, which is also a low-affinity, high-capacity hexokinase32 specific of the liver and the pancreatic β-cell. The kinetic characteristics of the system GLUT-2/glucokinase allows phosphorylation of glucose proportionally to its portal concentration. Glucose-6-phosphate can then enter the glycogen synthetic pathway. This is called the direct pathway for glycogen synthesis (Figure 7). However, numerous experiments have suggested that part of the glucose could be first degraded in peripheral tissues to 3-carbon substrates such as lactate, reach the liver, enter the gluconeogenic pathway up to the glucose-6-phosphate stage, and then be incorporated into glycogen. This is called the indirect pathway which involves an active phosphoenolpyruvate carboxykinase (PEPCK), one of the key gluconeogenic enzymes33 (Figure 8). The physiological significance of this pathway could be that glucose will be converted to three-carbon precursors at the periphery only when the peripheral glycogen stores are replenished. In other words, peripheral glycogen stores would be replenished in priority.
Replicase
Published in Paul Pumpens, Single-Stranded RNA Phages, 2020
The presence of an RNA-dependent RNA polymerase in the lysates of the phage f2-infected E. coli cells was observed for the first time by Zinder's team (August et al. 1963). It was highly important that the pioneers of the replicase search introduced the classical replicase assay that contained (i) ribonucleoside triphosphates as substrates, (ii) phosphoenol pyruvate and phosphoenol pyruvate kinase as a nucleoside triphosphate generating system and a high concentration of potassium phosphate buffer to inhibit polynucleotide phosphorylase activity, and (iii) deoxyribonuclease to inhibit the DNA dependent-RNA polymerase activity. With this assay there was virtually no incorporation of ribonucleotides into acid-insoluble material when extracts were prepared from uninfected cells. Moreover, August et al. (1963) observed for the first time the overproduction of the replicase activity by nonpolar coat protein amber mutant f2 sus11 and the absence of this activity by the polar coat protein amber mutant f2 sus3 infection in nonpermissive cells. The activity represented the existence of the template−enzyme complexes in the infected cells, but it appeared highly difficult to purify the stable template-dependent f2 enzyme (August et al. 1965; Shapiro and August 1965a,b), as it was managed later by the group III and IV phages.
Biogeneration of Volatile Organic Compounds in Microalgae-Based Systems
Published in Gokare A. Ravishankar, Ranga Rao Ambati, Handbook of Algal Technologies and Phytochemicals, 2019
Pricila Nass Pinheiro, Karem Rodrigues Vieira, Andriéli Borges Santos, Eduardo Jacob-Lopes, Leila Queiroz Zepka
In general, microalgae are commonly grown by converting dissolved, inorganic carbon (CO2) and absorbing solar energy. They have pigments such as chlorophyll and carotenoids, and in some cases phycobiliproteins which are involved in capturing luminous energy to perform photosynthesis. For the CO2 converted into carbohydrates, catalyzed by the enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), this process is referred to as the Calvin cycle. The Calvin cycle is the metabolic mechanism for fixing CO2 in microalgae. This process comprises three stages; carboxylation, reduction, and regeneration. The end of the cycle forms one molecule of glyceraldehyde-3-phosphate that through the action of enzymes forms phosphoenolpyruvate, and finally pyruvate (Santos et al. 2016a).
An evaluation of mitapivat for the treatment of hemolytic anemia in adults with pyruvate kinase deficiency
Published in Expert Review of Hematology, 2022
Andrew B. Song, Hanny Al‐Samkari
Pyruvate kinase deficiency (PKD) is a hereditary red blood cell (RBC) disorder that causes chronic hemolytic anemia. PKD was first discovered in the 1960s through a series of seminal studies clarifying the link between glycolysis, hemolytic anemia, and the specific deficiency of the pyruvate kinase enzyme [1–4]. We now understand that the pathogenesis of PKD is due to autosomal recessive mutations in the PKLR gene encoding the RBC pyruvate kinase enzyme. There are four PK isoenzymes in total: the PKLR gene encodes the L (liver) and R (RBC) isoenzymes, while the PKM gene encodes the M1 and M2 (muscle) isoenzymes. As the final enzymatic step in glycolysis, the PK enzyme catalyzes conversion of phosphoenolpyruvate (PEP) to pyruvate. Because mature RBCs are not capable of aerobic metabolism and largely rely on glycolysis for critical anaerobic generation of ATP, abnormalities in PK activity result in RBC ATP deficiency causing RBC dehydration, loss of cell membrane plasticity, and ultimately premature destruction by hemolytic anemia and ineffective erythropoiesis. Reticulocytes are exceptionally susceptible to dehydration and injury in the hypoxic spleen due to the transition from oxidative phosphorylation to glycolysis requiring large amounts of ATP [5].
Targeting endothelial cell metabolism in cancerous microenvironment: a new approach for anti-angiogenic therapy
Published in Drug Metabolism Reviews, 2022
Parisa Mohammadi, Reza Yarani, Azam Rahimpour, Fatemeh Ranjbarnejad, Joana Mendes Lopes de Melo, Kamran Mansouri
Pyruvate kinase (PK) catalyzes the last step of glycolysis and converts phosphoenolpyruvate and ADP to pyruvate and ATP. The M2 isoform of the four PK isoforms is predominant in ECs, either quiescent cells or proliferating cells, and its role is completely contact-dependent. Boa Kim et al. demonstrated that in proliferating ECs, PKM2 suppresses p53 gene expression and maintains cell cycle progression, while in contact-inhibited (quiescent) ECs is essential for maintaining vascular integrity so that inhibition of PKM2 leads to NFkB nuclear localization and upregulation of angiopoietin 2, a protein responsible for vascular leakage. Both functions are performed through the non-canonical role of PK enzyme. The expression of PKM2 is not affected by VEGF in ECs. Because PKM2-targeted adjuvant therapy predisposes patients who had been immunocompromised to sepsis, one needs to be cautious about this approach (Kim et al. 2018).
Investigation of anticancer activities of STA-9090 (ganetespib) as a second generation HSP90 inhibitor in Saos-2 osteosarcoma cells
Published in Journal of Chemotherapy, 2021
ATPase activity of HSP90 was measured by coupled enzyme assay (pyruvate kinase/lactate dehydrogenase).19,20 This assay is based on measurement of the consumption of NADH. Basically, pyruvate and ATP are generated from phosphoenolpyruvate (PEP) by pyruvate kinase (PK). Pyruvate is converted to lactate by lactate dehydrogenase (LDH) and NADH is oxidized to NAD+. In this assay, 10 µg/ml pure nucleotide free HSP90 was incubated at 37 °C for 5 min in 500 ml, pH 7.4 reaction mixture (50 mM HEPES, 50 mM NaCl, 4 mM MgCl2, 0.2 mM NADH, 0.5 mM PEP, 18 unit LDH, 24 unit PK/mL). The IC50 dose of STA-9090 (10.25 µM) and 0.5 mM ATP were added in the reaction mixture and optical density was measured at 340 nm. The ATPase activity of HSP90 in the absence of STA-9090 assumed 100% ATPase activity and inhibitory effect of STA-9090 were determined proportionally.