NAD and NADH are converted into each other in numerous different metabolic activities. In some metabolic reactions it is NAD which is the needed catalyst, with NADH a useful by-product, in other reactions the situation is reversed. NAD and NADH also serve to activate various enzymes, NAD for example, activates alcohol dehydrogenase and acetaldehyde dehydrogenase that are the two enzymes needed to detoxify the alcohol we drink into carbon dioxide and water. A coenzyme is the active, or working form of a vitamin. NADH is the reduced (electron- energy rich) coenzyme form of vitamin B3, while NAD is the oxidized (burned) coenzyme form of B3.
NADH is the first of five enzyme complexes of the electron transport chain, where much of the ATP bioenergy that runs every biological process of our lives is formed. As already noted, NAD is the coenzyme or active form of vitamin B3. The chemistry of NAD is some of the most complex in the human body. NAD is necessary to oxidize (burn) all foodstuffs (fats, sugars, amino-acids) into ATP bioenergy. There are three interlinked energy production cycles: the glycolytic (sugar burning) and Krebsí citric acid cycles (aminos and fats are "burned" through the Krebsí cycle), and the electron transport side chain.
NADH is extremely important to good health. The reason that it hasn't been widely discussed before is that until now, there was no way to do anything about improving the level of NADH in cells. While there is no such thing as a singularly most important compound in the body, or even a most important antioxidant, NADH comes as close as a single compound can. NADH is being tested to measure and see if it may increase athletic endurance Even the most healthy individuals will benefit from an increase in NADH levels. NADH can also help with sleep deprivation and jet lag. NADH Dehydrogenase is the largest of the respiratory complexes, the mammalian enzyme containing 45 separate polypeptide chains. Of particular functional importance are the flavin prosthetic group and eight iron-sulfur clusters (FeS). Of the 45 subunits, seven are encoded by the mitochondrial genome The structure is an "L" shape with a long membrane domain (with around 60 trans-membrane helices) and a hydrophilic peripheral domain, which includes all the known redox centres and the NADH binding site. Whereas the structure of the eukaryotic complex is not well characterised, the peripheral/hydrophilic domain of the complex from a bacterium.