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The NAD+/NADH coenzyme couple act as an electron reservoir for metabolic redox reactions, carrying electrons from one reaction to another. [5] Most of these metabolism reactions occur in the mitochondria. To regenerate NAD+ for further use, NADH pools in the cytosol must be reoxidized.
In cellular metabolism, NAD is involved in redox reactions, carrying electrons from one reaction to another, so it is found in two forms: NAD + is an oxidizing agent, accepting electrons from other molecules and becoming reduced; with H +, this reaction forms NADH, which can be used as a reducing agent to donate electrons.
Ferredoxin: NADP + reductase is the last enzyme in the transfer of electrons during photosynthesis from photosystem I to NADPH. [2] The NADPH is then used as a reducing equivalent in the reactions of the Calvin cycle. [2] Electron cycling from ferredoxin to NADPH only occurs in the light in part because FNR activity is inhibited in the dark. [11]
Dehydrogenase enzymes transfer electrons from the substrate to an electron carrier; what carrier is used depends on the reaction taking place. Common electron acceptors used by this subclass are NAD +, FAD, and NADP +. Electron carriers are reduced in this process and considered oxidizers of the substrate.
"P" here means pigment, and the number following it is the wavelength of light absorbed. Electrons in pigment molecules can exist at specific energy levels. Under normal circumstances, they are at the lowest possible energy level, the ground state. However, absorption of light of the right photon energy can lift them to a higher energy level.
NAD + kinase (EC 2.7.1.23, NADK) is an enzyme that converts nicotinamide adenine dinucleotide (NAD +) into NADP + through phosphorylating the NAD + coenzyme. [6] NADP + is an essential coenzyme that is reduced to NADPH primarily by the pentose phosphate pathway to provide reducing power in biosynthetic processes such as fatty acid biosynthesis and nucleotide synthesis. [7]
Anaerobic cellular respiration and fermentation generate ATP in very different ways, and the terms should not be treated as synonyms. Cellular respiration (both aerobic and anaerobic) uses highly reduced chemical compounds such as NADH and FADH 2 (for example produced during glycolysis and the citric acid cycle) to establish an electrochemical gradient (often a proton gradient) across a membrane.
Photosystem I (PSI, or plastocyanin–ferredoxin oxidoreductase) is one of two photosystems in the photosynthetic light reactions of algae, plants, and cyanobacteria. Photosystem I [1] is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ferredoxin.