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The effects of the NAD + /NADH ratio are complex, controlling the activity of several key enzymes, including glyceraldehyde 3-phosphate dehydrogenase and pyruvate dehydrogenase. In healthy mammalian tissues, estimates of the ratio of free NAD + to NADH in the cytoplasm typically lie around 700:1; the ratio is thus favorable for oxidative reactions.
A flavoprotein is a protein that contains a flavin group, which may be in the form of FAD or flavin mononucleotide (FMN). Many flavoproteins are known: components of the succinate dehydrogenase complex, α-ketoglutarate dehydrogenase, and a component of the pyruvate dehydrogenase complex.
The cofactors NAD + and FAD are sometimes reduced during this process to form NADH and FADH 2, which drive the creation of ATP in other processes. [15] A molecule of NADH can produce 1.5–2.5 molecules of ATP, whereas a molecule of FADH 2 yields 1.5 molecules of ATP. [16]
The last process in aerobic respiration is oxidative phosphorylation, also known as the electron transport chain. Here NADH and FADH 2 deliver their electrons to oxygen and protons at the inner membranes of the mitochondrion, facilitating the production of ATP. Oxidative phosphorylation contributes the majority of the ATP produced, compared to ...
Nicotinamide adenine dinucleotide phosphate, abbreviated NADP [1] [2] or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent ('hydrogen source').
The reducing agents NADH, NADPH, and FADH 2, [9] as well as metal ions, [4] act as cofactors at various steps in anabolic pathways. NADH, NADPH, and FADH 2 act as electron carriers , while charged metal ions within enzymes stabilize charged functional groups on substrates .
Hugo Theorell and coworkers showed that a bright-yellow-coloured yeast protein, identified previously as essential for cellular respiration, could be separated into apoprotein and a bright-yellow pigment. Neither apoprotein nor pigment alone could catalyse the oxidation of NADH, but mixing of the two
While the pentose phosphate pathway does involve oxidation of glucose, its primary role is anabolic rather than catabolic. The pathway is especially important in red blood cells (erythrocytes). The reactions of the pathway were elucidated in the early 1950s by Bernard Horecker and co-workers. [2] [3] There are two distinct phases in the pathway.