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[2] [3] There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of five-carbon sugars. For most organisms, the pentose phosphate pathway takes place in the cytosol; in plants, most steps take place in plastids. [4]
Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as any drug ...
Phosphorylation of glucose is a key reaction in sugar metabolism. The chemical equation for the conversion of D-glucose to D-glucose-6-phosphate in the first step of glycolysis is given by: D-glucose + ATP → D-glucose 6-phosphate + ADP ΔG° = −16.7 kJ/mol (° indicates measurement at standard condition)
Some textbooks combine the first two phases as the drug is often administered in an active form, which means that there is no liberation phase. Others include a phase that combines distribution, metabolism and excretion into a disposition phase. Other authors include the drug's toxicological aspect in what is known as ADME-Tox or ADMET.
Xenobiotic metabolism is divided into three phases. In phase I, enzymes such as cytochrome P450 oxidases introduce reactive or polar groups into xenobiotics. These modified compounds are then conjugated to polar compounds in phase II reactions. These reactions are catalysed by transferase enzymes such as glutathione S-transferases.
Substrate-level phosphorylation exemplified with the conversion of ADP to ATP. Substrate-level phosphorylation is a metabolism reaction that results in the production of ATP or GTP supported by the energy released from another high-energy bond that leads to phosphorylation of ADP or GDP to ATP or GTP (note that the reaction catalyzed by creatine kinase is not considered as "substrate-level ...
A Phase IV trial is also known as a postmarketing surveillance trial or drug monitoring trial to assure long-term safety and effectiveness of the drug, vaccine, device or diagnostic test. [1] Phase IV trials involve the safety surveillance (pharmacovigilance) and ongoing technical support of a drug after it receives regulatory approval to be ...
Isotopic labeling experiments have confirmed that this reaction proceeds through a glucose 1,6-bisphosphate intermediate. [2] The first step in the forward reaction is the transfer of a phosphoryl group from the enzyme to glucose 1-phosphate, forming glucose 1,6-bisphosphate and leaving a dephosphorylated form of the enzyme. [2]