NADH is the abbreviation for nicotinamide adenine dinucleotide. The ‘H’ stands for hydrogen and indicates that it is the reduced form of coenzyme #1. It's called coenzyme #1 because it ranks highest in importance above all other coenzymes in the body.

What is a coenzyme?
A coenzyme is any of a group of relatively small organic molecules that make up the non-protein portion of an enzyme and without which -- the enzyme is inactive. Coenzymes participate in chemical reactions catalyzed by enzymes. Although coenzymes are often structurally altered in the course of the reaction, coenzymes should always be restored to their original form. We don't know why or how coenzymes are depleted from the body.

Notable coenzymes include NADH and ATP adenosine triphosphate. Both are important in the creation and transfer of chemical energy. Coenzymes are vital to a variety of biochemical reactions in the body especially during respiration when the body uses the air it breathes.

For that matter, what is an enzyme?
Enzymes catalyze biological processes and also create products (molecules) in our body which we need to survive. Enzymes can be compared with production machinery which turns one material into another one. Like gasoline is turned into horsepower.

In living cells, enzymes catalyze the breakdown and turnover of food into smaller usable units called glucose. It is enzymes that have prepared the fuel the body uses for energy. Other enzymes transport the glucose (the fuel) into the cell. Once in the cell, it is coenzyme #1 that converts glucose (the fuel) into energy. In other words, it is coenzyme #1 that sparks the fuel, which creates the horsepower.

Enzymes can perform their work only if an additional coenzyme combines with the enzyme itself. Without the complementary coenzyme many enzymes do not work.

Clinical studies have shown a deficit in a coenzyme slows down an enzymes' ability to work. Other clinical studies have shown that a surplus of coenzymes increases the output of the enzymes work load. In other words, the enzymes (that are made by the body) has the power to perform its original workload when a sufficient supply of coenzymes are available (coenzymes are not made by the body).

For our readers, who want it in scientific terms
Coenzyme #1: NADH
The content of NADH is high in organisms with high production and energy requirements. The bulk of this occurs in the cytosol, where NADH is enclosed in the mitochondria. The microsomes and the nucleus contain only minimum amounts of NADH. NADH and NAD+ as well as nicotinamide are transported in the blood from one organ to the other.

To date, the central question has been: can NADH penetrate the cell membrane? If the answer is yes, the next question is, is NADH incorporated by a cell?

Using radio-labeled NADH, Dr. Birkmayer could demonstrate that NADH is able to cross the cell membrane because a considerable amount of it was found not only in cytoplasm, but also in the mitochondria and the nuclei.

The function of NADH in the cell takes place in the cytosol and in the mitochondria. The NADH dehydrogenase of the inner mitochondrial membrane can take-up electrons only from NADH in the cytosolic matrix. The inner membrane of mitochondria, however, is impermeable for cytosolic NADH. Special shuttle systems transport reduction equivalents from cytosolic NADH into the mitochondria. The most active of these systems is the maleate aspartate shuttle which occurs in heart, liver, and kidney mitochondria.

The reduction of equivalents of cytosolic NADH are transferred to the cytosolic oxaloacetate forming maleate by activity of cytosolic maleate dehydrogenase. Maleate can be transported through the mitochondrial membrane. There, the reduction equivalents are transferred to NAD+ by the enzyme, maleate dehydrogenase, producing NADH. This NADH donates its electrons directly into the respiratory chain. By donating one pair of electrons to the oxygen, 3 molecules of ATP are formed. In skeleton muscles and brain tissue the shuttle system is the glycerol phosphate instead of maleate.

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