Coenzyms



Coenzymes are relatively simple biochemical compounds that fulfil a role in enzymatic reactions. An enzyme needs a particular coenzyme to accelerate a reaction. On this page a few coenzymes are described.


                                                ATP
                                                Coenzyme A
                                                FAD
                                                GTP
                                                NAD+
                                                NADP+
                                                PLP
                                                TPP



ATP



Chemical name: Adenosine triphosphate
Abbreviation: ATP
Molecular formula: C10H16N5O13P3
Molecular weight: 507,183 g/mole

This compound consists of 3 phosphate-, 1 ribose- and 1 adenine molecule.
This molecule is a carrier of energy in biological systems.
The energy is located in the phosphate bonds. ATP can be converted in ADP (Adenosine Di phosphate) and ADP can finally be converted in AMP (Adenosine mono phosphate). In these conversions a phosphate bond is broken. When breaking such a phosphate bond chemical energy is released that can be used for something else again.


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Coenzyme A



Chemical name: Coenzyme A
Abbreviation: CoA or CoASH
Molecular formula: C21H36N7O16P3S
Molecular weight: 767,532 g/mole

Coenzyme A is a molecule that consists of Pantothenic acid (Vitamin B5), 3 phosphate-, ribose- and adenine molecules. It is active in decarboxylation reactions in the citric acid cycle. The thiol-group (sulphur-ester) in the CoA-SH molecule is the active part of the molecule. The rest of the molecule is involved in the binding to the right enzyme.
Coenzyme A plays an important role in the metabolism of fats, carbohydrates ( citric acid cycle) and proteins.


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FAD


Chemical name: Flavin adenine dinucleotide
Oxidised form.
Abbreviation: FAD
Molecular formula: C27H31N9O15P2
Molecular weight: 783,540 g/mole

Flavin adenine dinucleotide is a molecule that consists of: Riboflavine (vitamin B2) -, pyrophosphate-, ribose- and adenine molecules.
It is active as redox potential, this means that in this molecule energy can be stored in the form of hydrogen molecules (electrons). It is active in the citric acid cycle and other pathways.
The molecule can take up 2 electrons (H-) in oxidation reactions:
FAD + 2H- FADH2


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GTP



Chemical name: 5 '- Guanylate triphosphate
Abbreviation: GTP
Molecular formula: C10H16N5O14P3
Molecular mass: 523,183 g/mole

GTP is a molecule that consists of 3 phosphate-, ribose- and guanine molecules.
Carrier of energy in biological systems.


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NAD +



Chemical name: nicotinamide adenine dinucleotide, oxidised form.
Abbreviation: NAD+
Molecular formula: C21H27N7O14P2
Molecular weight: 663,430 g/mole

NAD+ is a molecule that consists of nicotinamide (Vitamin B3) -, pyrophosphate-, ribose- and adenine molecules.
This coenzyme is active as a redox potential, this means that in this molecule energy can be stored in the form of hydrogen molecules (electrons). It is active in breakdown reactions (catabolism) like the citric acid cycle.
The molecule can take up one electrons (H-) by oxidation reactions:
NAD+ + H- NADH
The NADH can become converted in the oxidative phosphorylation pathway into ATP.


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NADP+



Chemical name: nicotinamide adenine dinucleotide phosphate, oxidised form.
Abbreviation: NADP+
Molecular formula: C21H26N7O17P3
Molecular weight: 741,389 g/mole

NADP+ is a molecule that consists of nicotinamide (Vitamin B3) -, pyrophosphate-, ribose- and adenine molecules.
This coenzyme is active as a redox potential, this means that in this molecule energy can be stored. It is, in contrast to NAD, active in biosynthetic reactions (build-up reactions or anabolism). The two different coenzymes for the anabolism (build-up) and catabolism (break down) is to separate this two different process from each other.


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PLP



Chemical name: Pyridoxal 5-phosphate
Abbreviation: PLP
Molecular formula: C8H10NO6P
Molecular weight: 247.14 g/mole

PLP is a molecule that consists of Pyridoxine (Vitamin B6) and a phosphate group.
This coenzyme is active in the glycogen metabolism in particular in the glycogen breakdown. PLP together with the enzyme phosphorylase is responsible for the breakdown of glycogen.


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TPP



Chemical name: thiamin pyrophosphate or Thiamine diphosphate
Abbreviation: TPP or TDP
Molecular formula: C12H19N4O7P2S
Molecular weight: 425.316 g/mole

TPP is a molecule that consists of Thiamine (vitamin B1) and pyrophosphate (2 phosphates).
This coenzyme prepare pyruvate at the end of the glycolysis for the further breakdown in the citric acid cycle. It is active as a unit of the enzyme pyruvate dehydrogenase complex. Together with this enzyme it catalyse the decarboxylation (= to split a carbon atom off) of pyruvate.
It is also a part of the enzyme alpha-ketoglutarate dehydrogenase complex that is active in the citric acid cycle. In that way it regulates especially the carbohydrate breakdown were energy is obtained.





[1]. Stryer, Lubert;- Biochemistry - fourth edition; New York: W. H. Freeman and Company
(1995). ISBN 0-7167-2009-4



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