Coenzyme is a large class of organicCofactorIs the general name ofEnzyme catalysisRedox reactionGroup transfer and isomerization.They areEnzyme catalyzed reactionIt is used to transfer electrons, atoms or groups.Coenzyme can also be regarded as the second substrate, because it can be used incatalytic reactionWhen it occurs, the chemical change of coenzyme is just opposite to that of substrate.[1]
Coenzyme is a kind of enzyme that can transfer chemical groups from one enzyme to anotherOrganic small molecule, loosely combined with enzymes, which is necessary for the activity of specific enzymes.There are manyvitaminAnd its derivatives, such asThiamineandfolic acid, are coenzymes.These compounds cannot be synthesized by the human body and must be supplemented through diet.Different coenzymes can carry different chemical groups:NAD+OrNADP+Carrying reducing hydrogen,Coenzyme AcarryacetylFolic acid carries formyl group,S-adenosylmethionineCan also be carriedFormyl group。
Because coenzymeEnzyme catalysisThe chemical composition of coenzyme has changed during the reaction, so coenzyme can be considered as a special substrate or "second substrate".This so-called second substrate can be used by many enzymes.For example, about 700 enzymes are known to utilize coenzymesNADHCatalysis.
Some coenzymes containing adenosine (CoA, NAD+, FAD)[4]
The chemical name is nicotinamideadenineDinucleotide or twophosphoric acidNicotin, atmammalThere are oxidized (NAD+) and reduced forms in the body（NADH）Two states are important coenzymes in human redox reaction.At the same time, it is a NAD+dependent ADP coreGlycosyltransferaseThe only substrate of this enzyme in vivo mainly includes three types: 1. ADPRiboseGroup transferase or polyribosyl polymerase（PARP）；2. cADPR syntheses;3. III protein typeLysineDeacetylase Sirtuins.These enzymes willCoenzyme I(NAD+), as a substrate, decomposes into ADP ribose and nicotinamide (Nam), which play different roles in different cellsphysiological function[3]。
FMN and FAD are a seriesFlavinConnectedOxidoreductaseCoenzymes, or flavoproteins, from their interaction withEnzyme proteinIt can also be considered asCofactor。Some of these enzymes need some metals in addition to FMN or FADCofactor, such as iron or molybdenum ions.So they are calledMetalloflavin。These enzymes catalyze a series of reversible or irreversible redox reactions in cells.
Pyridoxal
Pyridoxal、PyridoxamineandPyridoxineCollectively referred to asVitamin B6(The structural formula of [vitamin structural formula] in Figure 3 is "class=image").Vitamin B6 is involved in the formation of two coenzymes, namely pyridoxal phosphate and pyridoxamine phosphate.
Originally used as yeastgrowth factorIs separated.Due to its widespread existence in living things, it is calledPantothenic acid。The coenzyme form of pantothenic acid isCoenzyme A(CoA or CoASH), a cofactor of enzymatic acetylation (Fig. 5 [Coenzyme A'sStructural]), which is biologically important asacylIts carrier or donor is very important in metabolism, especially in fatty acid metabolism.
folic acid
Because the earliestSpinachThe leaves are separated from each other, hence the name.
In the 1920s, it was found that the liver energy therapy of feeding animals to patientsPernicious anemia, indicating that there is a kind ofFactor pairPernicious anemia is effective.Vitamin B12Has beenSeparation and purificationAnd the structure has been clarified.Vitamin B12There is one in the structure ofGoolin(corrin) ring system containing cobalt ions andCyano group(CN), so it is also calledCyanocobalamin。PureVitamin B12 Solution It is red, which is also the characteristic of common cobalt compounds.As coenzyme, CN in vitamin B12 is 5 '-DeoxyadenosineSubstituted by the group, calledCoenzyme B12。This is an unstable compoundcyanideIt is converted to vitamin B12 in the presence or exposure to light.If 5 '- deoxyadenosine is used to replace the blackbody CN group in the formulaCoenzyme B12The structural formula of.
1. Coenzyme Q (CoQ) Coenzyme Q is a kind of quinone widely distributed in organisms, also known as ubiquinone.Exists inMitochondrial intimaMiddle, it's a creatureOxidative respiratory chainIt is an indispensable hydrogen transmitter, and has important physiological significance.Coenzyme QSide chainOfisopreneThe length of the unit for differentBiological speciesIt can be different.
4、vitamin KSome members of the vitamin K family may play some coenzyme roles in organisms.As coenzymeglutamateSome clues have been obtained about the function of carboxylation of residues.
According to enzymecatalytic reactionIn principle, a certain amount ofCofactor。Cofactors refer to a kind of nonproteinIngredients, including coenzymes, cofactors andmetal ionactivator.Enzyme boundCofactorCalled auxiliary basis;The enzyme protein without cofactor is calledApoenzyme protein（apoenzyme）, Nocatalytic activity, sufficient auxiliary bases must be added to formHoloenzyme（holoenzyme）, it has catalytic activity.After incubation with the coenzyme for a period of time,enzymatic activityTherefore, it is often necessary to pre incubate the sample with the auxiliary group in the reagent.The amount of auxiliary base is often small.
Coenzymes are loosely bound to enzyme proteins and can be easily separated from them by dialysis and other methods.Although coenzyme is different from enzyme substrateAction modeIt is similar to the substrate onEnzyme reaction processIt combines with enzyme, separates and circulates repeatedly.The coenzyme dosage can be determined by treating them as substrate.for examplelactate dehydrogenaseCoenzyme according to double substratekinetic equationcalculation.
Activator（activator）OfChemical essenceIt is a metal ion, which can beActive center of enzyme, or through other mechanismsActivating enzymeActivity.The influence of metal ions as activatorEnzymatic reactionThe dynamics of are more complex.The most common is divalent metal ions such as Mg2+Zn2+, Mn2+, Ca2+, Fe2+, etc.Heavy metal ions are mostly enzymaticDenaturant。Metal ions often antagonize or inhibit each other.Frequently addEDTAThe purpose is to chelate some unnecessary ions.Suitable metalIon concentrationIt is necessary. Excess ions often inhibit the enzymereaction rate 。Since the kinetics of activator is often different from that of enzyme, this can explain the different proportions of sample and reaction solution, resulting inEnzyme activity measurementThe results are not proportional.N-Acetylcysteineyescreatine kinaseOfActivationSimilar.The amount of activator is generally determined through repeated experiments.
5. Can be activatedHuman cellsAnd cell energy nutrition, which can improve human immunity, enhance anti-oxidationDelay senilityAnd enhance human vitality.In addition, there is antiadriamycinOfCardiotoxic effectsAnd protecting the liver.[2-3]
