- synthesis of organic substances from carbon dioxide and water with the obligatory use of light energy:
6CO 2 + 6H 2 O + Q light → C 6 H 12 O 6 + 6O 2.
In higher plants, the organ of photosynthesis is the leaf, and the organelles of photosynthesis are the chloroplasts (structure of chloroplasts - lecture No. 7). The membranes of chloroplast thylakoids contain photosynthetic pigments: chlorophylls and carotenoids. There are several different types of chlorophyll ( a, b, c, d), the main one is chlorophyll a. In the chlorophyll molecule, a porphyrin “head” with a magnesium atom in the center and a phytol “tail” can be distinguished. The porphyrin “head” is a flat structure, is hydrophilic and therefore lies on the surface of the membrane that faces the aqueous environment of the stroma. The phytol “tail” is hydrophobic and due to this retains the chlorophyll molecule in the membrane.
Chlorophylls absorb red and blue-violet light, reflect green light and therefore give plants their characteristic green color. Chlorophyll molecules in thylakoid membranes are organized into photosystems. Plants and blue-green algae have photosystem-1 and photosystem-2, while photosynthetic bacteria have photosystem-1. Only photosystem-2 can decompose water to release oxygen and take electrons from the hydrogen of water.
Photosynthesis is a complex multi-step process; photosynthesis reactions are divided into two groups: reactions light phase and reactions dark phase.
Light phase
This phase occurs only in the presence of light in thylakoid membranes with the participation of chlorophyll, electron transport proteins and the enzyme ATP synthetase. Under the influence of a quantum of light, chlorophyll electrons are excited, leave the molecule and enter the outer side of the thylakoid membrane, which ultimately becomes negatively charged. Oxidized chlorophyll molecules are reduced, taking electrons from water located in the intrathylakoid space. This leads to the breakdown or photolysis of water:
H 2 O + Q light → H + + OH - .
Hydroxyl ions give up their electrons, becoming reactive radicals.OH:
OH - → .OH + e - .
OH radicals combine to form water and free oxygen:
4NO. → 2H 2 O + O 2.
In this case, oxygen is removed to the external environment, and protons accumulate inside the thylakoid in the “proton reservoir”. As a result, the thylakoid membrane, on the one hand, is charged positively due to H +, and on the other, due to electrons, it is charged negatively. When the potential difference between the outer and inner sides of the thylakoid membrane reaches 200 mV, protons are pushed through the ATP synthetase channels and ADP is phosphorylated to ATP; Atomic hydrogen is used to restore the specific carrier NADP + (nicotinamide adenine dinucleotide phosphate) to NADPH 2:
2H + + 2e - + NADP → NADPH 2.
Thus, in the light phase, photolysis of water occurs, which is accompanied by three important processes: 1) ATP synthesis; 2) the formation of NADPH 2; 3) the formation of oxygen. Oxygen diffuses into the atmosphere, ATP and NADPH 2 are transported into the stroma of the chloroplast and participate in the processes of the dark phase.
1 - chloroplast stroma; 2 - grana thylakoid.
Dark phase
This phase occurs in the stroma of the chloroplast. Its reactions do not require light energy, so they occur not only in the light, but also in the dark. Dark phase reactions are a chain of successive transformations of carbon dioxide (coming from the air), leading to the formation of glucose and other organic substances.
The first reaction in this chain is the fixation of carbon dioxide; The carbon dioxide acceptor is a five-carbon sugar. ribulose biphosphate(RiBF); enzyme catalyzes the reaction Ribulose biphosphate carboxylase(RiBP carboxylase). As a result of carboxylation of ribulose bisphosphate, an unstable six-carbon compound is formed, which immediately breaks down into two molecules phosphoglyceric acid(FGK). A cycle of reactions then occurs in which phosphoglyceric acid is converted through a series of intermediates to glucose. These reactions use the energy of ATP and NADPH 2 formed in the light phase; The cycle of these reactions is called the “Calvin cycle”:
6CO 2 + 24H + + ATP → C 6 H 12 O 6 + 6H 2 O.
In addition to glucose, other monomers of complex organic compounds are formed during photosynthesis - amino acids, glycerol and fatty acids, nucleotides. Currently, there are two types of photosynthesis: C 3 - and C 4 photosynthesis.
C 3-photosynthesis
This is a type of photosynthesis in which the first product is three-carbon (C3) compounds. C 3 photosynthesis was discovered before C 4 photosynthesis (M. Calvin). It is C 3 photosynthesis that is described above, under the heading “Dark phase”. Characteristic features of C 3 photosynthesis: 1) the carbon dioxide acceptor is RiBP, 2) the carboxylation reaction of RiBP is catalyzed by RiBP carboxylase, 3) as a result of carboxylation of RiBP, a six-carbon compound is formed, which decomposes into two PGAs. FGK is restored to triose phosphates(TF). Some of the TF is used for the regeneration of RiBP, and some is converted into glucose.
1 - chloroplast; 2 - peroxisome; 3 - mitochondria.
This is a light-dependent absorption of oxygen and release of carbon dioxide. At the beginning of the last century, it was established that oxygen suppresses photosynthesis. As it turned out, for RiBP carboxylase the substrate can be not only carbon dioxide, but also oxygen:
O 2 + RiBP → phosphoglycolate (2C) + PGA (3C).
The enzyme is called RiBP oxygenase. Oxygen is a competitive inhibitor of carbon dioxide fixation. The phosphate group is split off and the phosphoglycolate becomes glycolate, which the plant must utilize. It enters peroxisomes, where it is oxidized to glycine. Glycine enters the mitochondria, where it is oxidized to serine, with the loss of already fixed carbon in the form of CO 2. As a result, two glycolate molecules (2C + 2C) are converted into one PGA (3C) and CO 2. Photorespiration leads to a decrease in the yield of C3 plants by 30-40% ( With 3 plants- plants characterized by C 3 photosynthesis).
C 4 photosynthesis is photosynthesis in which the first product is four-carbon (C 4) compounds. In 1965, it was found that in some plants (sugar cane, corn, sorghum, millet) the first products of photosynthesis are four-carbon acids. These plants were called With 4 plants. In 1966, Australian scientists Hatch and Slack showed that C4 plants have virtually no photorespiration and absorb carbon dioxide much more efficiently. The pathway of carbon transformations in C 4 plants began to be called by Hatch-Slack.
C 4 plants are characterized by a special anatomical structure of the leaf. All vascular bundles are surrounded by a double layer of cells: the outer layer is mesophyll cells, the inner layer is sheath cells. Carbon dioxide is fixed in the cytoplasm of mesophyll cells, the acceptor is phosphoenolpyruvate(PEP, 3C), as a result of carboxylation of PEP, oxaloacetate (4C) is formed. The process is catalyzed PEP carboxylase. Unlike RiBP carboxylase, PEP carboxylase has a greater affinity for CO 2 and, most importantly, does not interact with O 2 . Mesophyll chloroplasts have many grains where light phase reactions actively occur. Dark phase reactions occur in the chloroplasts of the sheath cells.
Oxaloacetate (4C) is converted to malate, which is transported through plasmodesmata into the sheath cells. Here it is decarboxylated and dehydrogenated to form pyruvate, CO 2 and NADPH 2 .
Pyruvate returns to the mesophyll cells and is regenerated using the energy of ATP in PEP. CO 2 is again fixed by RiBP carboxylase to form PGA. PEP regeneration requires ATP energy, so it requires almost twice as much energy as C 3 photosynthesis.
The meaning of photosynthesis
Thanks to photosynthesis, billions of tons of carbon dioxide are absorbed from the atmosphere every year and billions of tons of oxygen are released; photosynthesis is the main source of the formation of organic substances. Oxygen forms the ozone layer, which protects living organisms from short-wave ultraviolet radiation.
During photosynthesis, a green leaf uses only about 1% of the solar energy falling on it; productivity is about 1 g of organic matter per 1 m2 of surface per hour.
Chemosynthesis
The synthesis of organic compounds from carbon dioxide and water, carried out not due to the energy of light, but due to the energy of oxidation of inorganic substances, is called chemosynthesis. Chemosynthetic organisms include some types of bacteria.
Nitrifying bacteria ammonia is oxidized to nitrous and then to nitric acid (NH 3 → HNO 2 → HNO 3).
Iron bacteria convert ferrous iron into oxide iron (Fe 2+ → Fe 3+).
Sulfur bacteria oxidize hydrogen sulfide to sulfur or sulfuric acid (H 2 S + ½O 2 → S + H 2 O, H 2 S + 2O 2 → H 2 SO 4).
As a result of oxidation reactions of inorganic substances, energy is released, which is stored by bacteria in the form of high-energy ATP bonds. ATP is used for the synthesis of organic substances, which proceeds similarly to the reactions of the dark phase of photosynthesis.
Chemosynthetic bacteria contribute to the accumulation of minerals in the soil, improve soil fertility, promote wastewater treatment, etc.
Go to lectures No. 11“The concept of metabolism. Biosynthesis of proteins"
Go to lectures No. 13“Methods of division of eukaryotic cells: mitosis, meiosis, amitosis”
Coenzymes FMN (RMM) and FAD (RAO)
The biological role of flavin enzymes is that they catalyze aerobic redox reactions in living systems, for example, they oxidize reducing coenzymes - NADH2, NADPH2, which carry H2 in the respiratory chain.
Thiol coenzymes
Thiol coenzymes include the acylation coenzyme (CoA, CoA, HSCoA), the biological role of which is to transfer acyl groups. If CoA transfers acetyl (CH 3 CO–), then it is called an acetylation coenzyme. CoA contains vitamin B 3 (pantothenic acid):
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Acyl groups are transferred to CoA due to the ester bond of coenzyme A with the thiol group –SH.
The biological role of the acetylation coenzyme is that it is:
1) a key substance of intermediate metabolism, a carrier of CH 3 CO– groups, which enter the Krebs cycle for oxidation to H 2 O and CO 2 and energy generation;
2) a coenzyme involved in the biosynthesis and breakdown of fatty acids to amino acids.
SECTION 4. PHYSICAL AND CHEMICAL PROPERTIES OF ENZYMES
Enzymes– these are high-molecular compounds, amphoteric electrolytes, the characteristic properties of which are:
Hydrophilicity;
Salting out;
Denaturation;
Properties of colloidal systems;
Optimum pH;
Temperature optimum;
High specificity of action;
Activation and inhibition of enzymes.
Effect of temperature on enzyme activity
For enzymatic reactions, Van't Hoff's rule is true: with an increase in temperature by 10 °C, the reaction rate increases by 2–4 times:
,
where V t2 – speed at temperature t2; V t1 – speed at temperature t1; Δt= t2 – t1; γ = 2–4 – temperature coefficient.
This dependence is maintained up to a certain temperature level - the temperature optimum. For most enzymes, the temperature optimum is in the range of 35...45 °C. An increase in temperature above the optimum leads to a decrease in enzyme activity; at t > 70 °C the enzyme is inactivated, i.e., it loses its biological activity. Since the enzyme is a protein, when the temperature increases, it denatures, the structure of the active center changes, and as a result, the enzyme cannot react with the substrate. The exceptions are myokinase, which is active at 100 °C, and catalase, active at 0 °C.
Optimum pH
Enzymes exhibit maximum activity at the optimal physiological pH range (see Appendix). For example, the optimum pH for sucrase is 6.2, for pepsin – 1.5–2.5.
Reversibility of action
Some enzymes can catalyze forward and reverse reactions.
Specificity (selectivity) of action
An enzyme can catalyze one or more chemical reactions of similar nature. Specificity is based on the hypothesis of E. Fischer: strict correspondence between the structure of the substrate and the active center, like a key to a lock.
Specificity can be relative or absolute. Relative specificity characteristic of enzymes acting on a certain type of bond. Enzymes with relative specificity include esterases (hydrolysis based on the location of ester bonds) and proteinases (hydrolysis of the peptide bond).
Absolute specificity (absolute selectivity) is that the enzyme catalyzes the transformation of only one substrate of a specific structure.
For example:
Sucrose Sucrose
Arginase Arginine
Absolute specificity also includes stereochemical specificity, i.e., the effect of an enzyme on a specific stereoisomer.
Enzyme activation. Activators. Inhibition. Inhibitors
Activation called an increase in enzyme activity activators– substances that increase enzyme activity.
Activators can be metal ions (Na +, K +, Mg 2+).
One type of activation process is the process of enzyme self-activation. Enzymes have proenzymes (zymogens)– inactive forms of enzymes, when the active center is masked by an additional section of the peptide chain, as a result of which the substrate cannot approach the active center. The transformation of a zymogen into an active enzyme as a result of the removal of a section of the peptide chain and the release of the active center is called self-activation.
A decrease in the rate of an enzymatic reaction under the influence of inhibitors is called inhibition, respectively inhibitors– these are substances that inhibit the action of enzymes. Inhibitors are heavy metal ions, acids, alkalis, alcohols, etc.
Inhibition can be either reversible or irreversible.
At irreversible When inhibited, the enzyme loses its activity completely due to destruction of the structure (denaturation). Inhibitors include denaturing physical and chemical factors.
Reversible inhibition is the reversible interaction of an enzyme with a substrate. Reversible inhibition can be competitive or noncompetitive.
At competitive In reversible inhibition, “competition” occurs between the substrate and the inhibitor for interaction with the active center of the enzyme.
Substrate and inhibitors are structural analogues. The inhibitor (I), competing with the substrate (S), forms an inhibitor-enzyme complex (EU) with the enzyme (E):
E + S + U ↔ EU + S
nnginttorno-
enzymatic
complex
Non-competitive or allosteric(from Greek allos– another), Inhibition is based on the fact that the inhibitor is not a structural analogue of the substrate and binds not to the active, but to the allosteric center, as a result of which the structure of the enzyme changes, and the active center cannot attach the substrate.
They play an important role in regulating the action of enzymes compartmentation, i.e. localization in subcellular structures.
Cyclic adenosine monophosphate (CAMP)- an ATP derivative that acts as a second messenger in the body, used for intracellular distribution of signals of certain hormones (for example, glucagon or adrenaline) that cannot pass through the cell membrane. Converts a number of inert proteins into enzymes (camp-dependent protein kinases), under the influence of which a number of biochemical reactions occur. reactions (conduction of nerve impulses).
cAMP production is stimulated adrenaline.
Cyclic guanosine monophosphate (cGMP) is a cyclic form of nucleotide formed from guanosine triphosphate (GTP) by the enzyme guanylate cyclase. Education is stimulated acetylcholine.
· cGMP is involved in the regulation of biochemical processes in living cells as a secondary messenger (second messenger). It is characteristic that many of the effects of cGMP are directly opposite to cAMP.
· cGMP activates G-kinase and phosphodiesterase, which hydrolyzes cAMP.
· cGMP is involved in the regulation of the cell cycle. The choice of the cell depends on the cAMP/cGMP ratio: stop dividing (stop in the G0 phase) or continue, moving to the G1 phase.
· cGMP stimulates cell proliferation (division), and cAMP suppresses
Adenosine triphosphate (ATP)- a nucleotide formed by a nitrogenous base adenine, the five-carbon sugar ribose and three phosphoric acid residues. The phosphate groups in the ATP molecule are connected to each other high-energy (macroergic) connections. The bonds between phosphate groups are not very strong, and when they break, a large amount of energy is released. As a result of hydrolytic cleavage of the phosphate group from ATP, adenosine diphosphoric acid (ADP) is formed and a portion of energy is released.
· Together with other nucleoside triphosphates, ATP is the starting product in the synthesis of nucleic acids.
· ATP plays an important role in the regulation of many biochemical processes. Being an allosteric effector of a number of enzymes, ATP, joining their regulatory centers, enhances or suppresses their activity.
· ATP is also a direct precursor for the synthesis of cyclic adenosine monophosphate, a secondary messenger of hormonal signal transmission into the cell.
· The role of ATP as a mediator in synapses and a signal substance in other intercellular interactions is also known
Adenosine Diphosphate (ADP)- a nucleotide consisting of adenine, ribose and two phosphoric acid residues. ADP is involved in energy metabolism in all living organisms; ATP is formed from it by phosphorylation:
ADP + H3PO4 + energy → ATP + H2O.
The cyclic phosphorylation of ADP and the subsequent use of ATP as an energy source form a process that is the essence of energy metabolism (catabolism).
FAD - flavin adenine dinucleotide- a coenzyme that takes part in many redox biochemical processes. FAD exists in two forms - oxidized and reduced, its biochemical function, as a rule, is to transition between these forms.
Nicotinamide adenine dinucleotide (NAD) - dinucleotide consists of two nucleotides connected by their phosphate groups. One of the nucleotides contains adenine as a nitrogenous base, the other contains nicotinamide. Nicotinamide adenine dinucleotide exists in two forms: oxidized (NAD) and reduced (NADH).
· In metabolism, NAD is involved in redox reactions, transferring electrons from one reaction to another. Thus, in cells, NAD exists in two functional states: its oxidized form, NAD+, is an oxidizing agent and takes electrons from another molecule, being reduced to NADH, which then serves as a reducing agent and donates electrons.
· 1. Metabolism of proteins, fats and carbohydrates. Since NAD and NADP serve as coenzymes of most dehydrogenases, they participate in the reactions
during the synthesis and oxidation of fatty acids,
during the synthesis of cholesterol,
exchange of glutamic acid and other amino acids,
carbohydrate metabolism: pentose phosphate pathway, glycolysis,
oxidative decarboxylation of pyruvic acid,
tricarboxylic acid cycle.
· 2. NADH performs a regulatory function because it is an inhibitor of certain oxidation reactions, for example, in the tricarboxylic acid cycle.
· 3. Protection of hereditary information - NAD is a substrate of poly-ADP-ribosylation in the process of cross-linking chromosomal breaks and DNA repair, which slows down necrobiosis and cell apoptosis.
· 4. Protection against free radicals - NADPH is an essential component of the cell's antioxidant system.
Coenzymes in catalytic reactions transport various groups of atoms, electrons or protons. Coenzymes bind to enzymes:
Covalent bonds;
Ionic bonds;
Hydrophobic interactions, etc.
One coenzyme can be a coenzyme for several enzymes. Many coenzymes are multifunctional (for example, NAD, PF). The specificity of the holoenzyme depends on the apoenzyme.
All coenzymes are divided into two large groups: vitamin and non-vitamin.
Coenzymes of vitamin nature– vitamin derivatives or chemical modifications of vitamins.
1st group: thiamine – vitamin B1 derivatives. These include:
Thiamine monophosphate (TMP);
Thiamine diphosphate (TDP) or thiamine pyrophosphate (TPP) or cocarboxylase;
Thiamine triphosphate (TTP).
TPF has the greatest biological significance. Part of the keto acid decarboxylase: PVK, a-ketoglutaric acid. This enzyme catalyzes the removal of CO 2.
Cocarboxylase participates in the transketolase reaction from the pentose phosphate cycle.
Group 2: flavin coenzymes, vitamin B2 derivatives. These include:
- flavin mononucleotide (FMN);
- flavin adenine dinucleotide (FAD).
Rebitol and isoaloxazine form vitamin B2. Vitamin B2 and the phosphorus residue form FMN. FMN combines with AMP to form FAD.
[rice. the isoaloxazine ring is connected to rebitol, rebitol to phosphorus, and phosphorus to AMP]
FAD and FMN are coenzymes of dehydrogenases. These enzymes catalyze the removal of hydrogen from the substrate, i.e. participate in oxidation–reduction reactions. For example, SDH - succinate dehydrogenase - catalyzes the transformation of succinic acid into fumaric acid. This is a FAD-dependent enzyme. [rice. COOH-CH 2 -CH 2 -COOH® (above the arrow - SDH, below - FAD and FADN 2) COOH-CH=CH-COOH]. Flavin enzymes (flavin-dependent DGs) contain FAD, which is the primary source of protons and electrons. In the process of chemical reactions FAD turns into FADN 2. The working part of FAD is the 2nd ring of isoaloxazine; in the process of chemical The reaction involves the addition of two hydrogen atoms to the nitrogens and the rearrangement of double bonds in the rings.
Group 3: pantothenic coenzymes, vitamin B3 derivatives– pantothenic acid. They are part of coenzyme A, NS-CoA. This coenzyme A is a coenzyme of acyltransferases, together with which it transfers various groups from one molecule to another.
Group 4: nicotinamide, derivatives of vitamin PP - nicotinamide:
Representatives:
Nicotinamide adenine dinucleotide (NAD);
Nicotinamide adenine dinucleotide phosphate (NADP).
The coenzymes NAD and NADP are coenzymes of dehydrogenases (NADP-dependent enzymes), for example malateDH, isocitrateDH, lactateDH. Participate in dehydrogenation processes and redox reactions. In this case, NAD adds two protons and two electrons, and NADH2 is formed.
Rice. working group NAD and NADP: drawing of vitamin PP, to which one H atom is attached and as a result a rearrangement of double bonds occurs. A new configuration of vitamin PP + H + ] is drawn
Group 5: pyridoxine derivatives of vitamin B6. [rice. pyridoxal. Pyridoxal + phosphorus = pyridoxal phosphate]
- pyridoxine;
- pyridoxal;
- pyridoxamine.
These forms are interconverted during reactions. When pyridoxal reacts with phosphoric acid, pyridoxal phosphate (PP) is obtained.
PF is a coenzyme of aminotransferases, transfers an amino group from AA to a keto acid - reaction transamination. Vitamin B6 derivatives are also included as coenzymes in AA decarboxylases.
Non-vitamin coenzymes- substances that are formed during metabolism.
1) Nucleotides– UTF, UDF, TTF, etc. UDP-glucose enters into glycogen synthesis. UDP-hyaluronic acid is used to neutralize various substances in transverse reactions (glucuronyl transferase).
2) Porphyrin derivatives(heme): catalase, peroxidase, cytochromes, etc.
3) Peptides. Glutathione is a tripeptide (GLU-CIS-GLY), it participates in reactions and is a coenzyme of oxidoreductases (glutathione peroxidase, glutathione reductase). 2GSH“(above arrow 2H) G-S-S-G. GSH is the reduced form of glutathione, and G-S-S-G is the oxidized form.
4) Metal ions, for example, Zn 2+ is part of the enzyme AlDH (alcohol dehydrogenase), Cu 2+ - amylase, Mg 2+ - ATPase (for example, myosin ATPase).
May participate in:
Attachment of the enzyme substrate complex;
In catalysis;
Stabilization of the optimal conformation of the active center of the enzyme;
Stabilization of quaternary structure.
Enzymes, like proteins, are divided into 2 groups: simple And complex. Simple ones consist entirely of amino acids and, upon hydrolysis, form exclusively amino acids. Their spatial organization is limited by the tertiary structure. These are mainly gastrointestinal enzymes: pepsin, trypsin, lysacym, phosphatase. Complex enzymes, in addition to the protein part, also contain non-protein components. These non-protein components differ in the strength of binding to the protein part (alloenzyme). If the dissociation constant of a complex enzyme is so small that in solution all polypeptide chains are associated with their non-protein components and are not separated during isolation and purification, then the non-protein component is called prosthetic group and is considered as an integral part of the enzyme molecule.
Under coenzyme understand an additional group that is easily separated from the alloenzyme upon dissociation. There is a rather complex covalent bond between the alloenzyme and the simplest group. There is a non-covalent bond (hydrogen or electrostatic interactions) between the alloenzyme and the coenzyme. Typical representatives of coenzymes are:
B 1 - thiamine; pyrophosphate (it contains B)
B 2 - riboflavin; FAD, FNK
PP - NAD, NADP
H – biotin; biositine
B 6 - pyridoxine; pyridoxal phosphate
Pantothenic acid: coenzyme A
Many divalent metals (Cu, Fe, Mn, Mg) also act as cofactors, although they are neither coenzymes nor prosthetic groups. Metals are part of the active center or stabilize the optimal structure of the active center.
METALSENZYMES
Fe, Fehemoglobin, catalase, peroxidase
Cu,Cu cytochrome oxidase
ZnDNA – polymerase, dehydrogenase
Mghexokinase
Mnarginase
Seglutathione reductase
ATP, lactic acid, and tRNA can also perform a cofactor function. One distinctive feature of two-component enzymes should be noted, which is that neither the cofactor (coenzyme or prosthetic group) nor the alloenzyme individually exhibit catalytic activity, and only their integration into a single whole, proceeding in accordance with the program of their three-dimensional organization, ensures rapid the occurrence of chemical reactions.
Structure of NAD and NADP.
NAD and NADP are coenzymes of pyridine-dependent dehydrogenases.
NICOTINAMIDE ADNINE DINE NUCLEOTIDE.
NICOTINAMIDE ADNINE DINE NUCLEOAMIDE PHOSPHATE (NADP)
The ability of NAD and NADP to play the role of an accurate hydrogen carrier is associated with the presence in their structure -
nicotinic acid reamide.
In cells, NAD-dependent dehydrogenases are involved
in the processes of electron transfer from the substrate to O.
NADP-dependent dehydrogenases play a role in the process -
sah biosynthesis. Therefore, the coenzymes NAD and NADP
differ in intracellular localization: NAD
concentrated in mitochondria, and most of the NADP
is located in the cytoplasm.
Structure of FAD and FMN.
FAD and FMN are prosthetic groups of flavin enzymes. They are very firmly attached to the alloenzyme, unlike NAD and NADP.
FLAVIN MONONUCLEOTIDE (FMN).
FLAVINACETYLDINUCLEOTIDE.
The active part of the FAD and FMN molecule is the isoalloxadine ring riboflavin, to the nitrogen atoms of which 2 hydrogen atoms can be attached.
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