烟酰胺腺嘌呤二核苷酸 NAD+

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人体核心氧化还原辅酶：作为 NAD+/NADH 电子载体参与线粒体三羧酸循环与氧化磷酸化，同时是 Sirtuins（去乙酰化酶）、PARP（DNA 修复）与 CD38 的底物，随龄下降，补充前体（NMN/NR）旨在提升其水平

生理基础功效
人体核心辅酶，参与全身上千种代谢反应：
细胞能量代谢：辅助线粒体分解糖、脂肪产生 ATP，改善疲劳、提升精力；
DNA 损伤修复：激活长寿蛋白 Sirtuins，减轻细胞氧化损伤；
神经保护：改善脑细胞代谢，缓解脑疲劳、辅助改善认知；
调节衰老相关炎症，改善皮肤老化、睡眠质量。

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine nucleobase and the other, nicotinamide. NAD exists in two forms: an oxidized and reduced form, abbreviated as NAD+ and NADH (H for hydrogen), respectively.

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. These electron transfer reactions are the main function of NAD. It is also used in other cellular processes, most notably as a substrate of enzymes in adding or removing chemical groups to or from proteins, in posttranslational modifications. Because of the importance of these functions, the enzymes involved in NAD metabolism are targets for drug discovery.

In organisms, NAD can be synthesized from simple building-blocks (de novo) from either tryptophan or aspartic acid, each a case of an amino acid. Alternatively, more complex components of the coenzymes are taken up from nutritive compounds such as vitamin B3 (also called niacin, or (nicotinic acid, hence the name "nicotinamide"). Similar compounds are produced by reactions that break down the structure of NAD, providing a salvage pathway that recycles them back into their respective active form.

In the name NAD+, the superscripted plus sign indicates the positive formal charge on one of its nitrogen atoms.

Some NAD is converted into the coenzyme nicotinamide adenine dinucleotide phosphate (NADP), whose chemistry largely parallels that of NAD, though its predominant role is as a coenzyme in anabolic metabolism.

Source: English Wikipedia, "Nicotinamide adenine dinucleotide".

Rossmann fold in part of the lactate dehydrogenase of Cryptosporidium parvum, showing NAD in red, beta sheets in yellow, and alpha helices in purple Nicotinamide adenine dinucleotide has several essential roles in metabolism. It acts as a coenzyme in redox reactions, as a donor of ADP-ribose moieties in ADP-ribosylation reactions, as a precursor of the second messenger molecule cyclic ADP-ribose, as well as acting as a substrate for bacterial DNA ligases and a group of enzymes called sirtuins that use NAD to remove acetyl groups from proteins. In addition to these metabolic functions, NAD emerges as an adenine nucleotide that can be released from cells spontaneously and by regulated mechanisms, and can therefore have important extracellular roles.

Oxidoreductase binding of NAD Further information: Protein structure and Oxidoreductase The main role of NAD in metabolism is the transfer of electrons from one molecule to another. Reactions of this type are catalyzed by a large group of enzymes called oxidoreductases. The correct names for these enzymes contain the names of both their substrates: for example NADH-ubiquinone oxidoreductase catalyzes the oxidation of NADH by coenzyme Q. However, these enzymes are also referred to as dehydrogenases or reductases, with NADH-ubiquinone oxidoreductase commonly being called NADH dehydrogenase or sometimes coenzyme Q reductase.

There are many different superfamilies of enzymes that bind NAD / NADH. One of the most common superfamilies includes a structural motif known as the Rossmann fold. The motif is named after Michael Rossmann, who was the first scientist to notice how common this structure is within nucleotide-binding proteins.

An example of a NAD-binding bacterial enzyme involved in amino acid metabolism that does not have the Rossmann fold is found in Pseudomonas syringae pv. tomato (PDB: 2CWH​; InterPro: IPR003767).

In this diagram, the hydride acceptor C4 carbon is shown at the top. When the nicotinamide ring lies in the plane of the page with the carboxy-amide to the right, as shown, the hydride donor lies either "above" or "below" the plane of the page. If "above" hydride transfer is class A, if "below" hydride transfer is class B.