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Bushra Ghnimat

Ayat Nabil

Name

NAme

#

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Oxidoreductases:

These enzymes catalyze oxidation & reduction reactions involving the transfer of

hydrogen atoms, electrons or oxygen

This group can be further divided into 4 main classes: 1) Dehydrogenases 2) Oxidases 3) Peroxidases 4) Oxygenases

1) Dehydrogenases

- Dehydrogenases catalyze hydrogen transfer from the substrate to a molecule known

as nicotinamide adenine dinucleotide (NAD+) ---> (most common electron recipient)

(they remove hydrogen, so they oxidize the substrate they have. When they remove

hydrogen, they will upload their electrons on electron acceptor (recipient)).

✓ The substrate will be oxidized and NAD+ will be reduced. - lactate dehydrogenase

dehydrogenasealcohol -

2) oxidases

Oxidases catalyze hydrogen transfer from the substrate to molecular oxygen producing

hydrogen peroxide as a by-product.

(they oxidize molecules using

molecular oxygen (O2))

➢ Glucose oxidase

It is always the electron recipient, unless you are otherwise informed Lactate is oxidized to pyruvate

Ethanol is oxidized to acetaldehyde.

Oxidizing of a carbohydrate produces lactone

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peroxidases 3)

-Peroxidases catalyze oxidation of a substrate by hydrogen peroxide.

EXAMPLE: Oxidation of two molecules of glutathione (GSH) in the presence of hydrogen

peroxide.

4) Oxygenases (they behave like oxidases, but the difference is that oxygen will not be coupled to hydrogen and get out in the product as a hydrogen peroxide. Oxygen is introduced inside the structure of the substrate)

▪ Oxygenases catalyze substrate oxidation by molecular O2. ▪ The reduced product of the reaction in this case is water and not hydrogen

peroxide ▪ There are two types of oxygenases Monooxygenases: introduce one oxygen atom to the substrate and reduce the other oxygen atom to water.

(Introducing one of the oxygens inside the substrate )

Dioxygenases: introduce both atoms of molecular oxygen (O2) into the product(s) of the reaction (Introducing both oxygens inside the substrate). - both enzymes are used for synthesis and degradation of heme in our bodies.

Dr said that he will bring enzymes that we have never heard of.

Don’t be afraid!

you should look at the enzyme and remember to which major class

and subclass refers, so you can understand what this enzyme does.

An oxidizing agent

Water will get out of the reaction as a product

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Transferases

- These enzymes transfer a functional group (C, N, P or S)from one substrate to an

acceptor molecule.

- it has two subclasses:

1) kinases (transfer of a phosphate group from one molecule to another. The most

common source for phosphate group is (ATP)

Phosphofructokinase: catalyzes transfer of phosphate from ATP to fructose-6

phosphate.

OR aminotransferasesransaminases T) 2

A transaminase transfers an amino functional group from one amino acid to a keto acid

(it has an acidic part and ketone part), converting the amino acid to a keto acid and the

keto acid to an amino acid.

-This allows for the interconversion of certain amino acids.

Ring of heme Two oxygens are inserted, and the

ring is broken, so it is dioxygenase

Amino acid Amino acid Keto acid Keto acid

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Their corresponding keto acids Amino acids pyruvate alanine

Alpha ketoglutaric acid OR Alpha keto glutarate

Glutamic acid

Oxaloacetate Aspartic acid Aspartate (4 C)

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Hydrolysis

- These enzymes catalyze cleavage reactions while using water across the bond being

broken.

-Peptidases, esterase, lipases, glycosidases, phosphatases and nucleases are all examples of hydrolases named depending on the type of bond cleaved.

- Proteases (also called peptidases) These enzymes catalyze proteolysis, the hydrolysis of a peptide bond within proteins.

➢ Proteolytic enzymes differ in their degree of substrate Specificity

➢ Trypsin, is quite specific; catalyzes the splitting of peptide bonds only on the carboxyl side of lysine and arginine

➢ Thrombin, catalyzes the hydrolysis of Arg-Glybonds in particular peptide sequences only.

------------------------------------------------------------------------------------------------------ lyases - Catalyze the addition or removal of functional groups from their substrates with the

associated formation or removal of double bonds between C-C, C-O and C-N

▪ Decarboxylases: is a subclass of lyases (it takes out the carboxylic group outside of any substrate releasing CO2 and forming a double bond)

▪ Aldolase: breaks down fructose-1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehydes-3-phosphate

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▪ Enolase: interconverts phosphoenolpyruvate (PEP) and 2-phosphoglycerate by

formation and removal of double bonds. → The enzyme before the last in the process of glycolysis.

------------------------------------------------------------------------------------------------------- Isomerases (mutases) → Mutases are subtype of isomerases. - Catalyze intermolecular rearrangements

➢ Glucose-6-phosphate isomerase: it isomerizes glucose-6-phosphate to fructose-6-phosphate (both are having the same numbers of C, O and H, but they differ in their structure or orientation in the space, so they are constitutional isomers or stereoisomers)

➢ Phosphoglycerate mutase: transfers a phosphate

group from carbon number 3 to carbon number 2 of phosphorylated glycerate (BPG

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Ligases(carboxylases) → Carboxylases are subtype of ligases.

• Ligases join C-C, C-O, C-N, C-S and C-halogen bonds (ligases are anabolic enzymes).

• The reaction is usually accompanied by the consumption of a high energy compound such as ATP.

Pyruvate carboxylase

3 carbon molecule

Inorganic phosphate

is released as a by-

product of the

reaction

4 carbon molecule

This is in the glycolytic process

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catalysis ----> ي تساعد اإلنزيم عىل العمل رح نحكي عن األشياء الت

-The side chains of amino acids are polar because there should be catalysis (binding and losing). -The hydrophobic interaction causes binding, but it doesn’t cause catalysis. --------------------------------------------------------------------------------------------------------------------- → Enzymes cofactors

gets in, it will be a carboxylic group. 2in any chemical reaction COWhenever you are seeing

leaving the reaction, it was in the molecule as a carboxylic group. 2whenever you are seeing CO

most enzymes require a non-proteinaceous part (a material that has nothing to do with amino acids. It is

not an amino acid in nature. it binds the enzyme and then now the enzyme is fully functional)

The things

that make

enzymes

work: Polar amino acids

Pka of side chain of histidine = physiological PH

▪ if they are tightly bound to the enzyme and if separated from it, the structure of the enzyme will be degraded or denatured we call it (prosthetic groups) . if they are loosely bound to the enzyme, come and go while the structure of the enzyme is preserved, we call

it (co-substrates).

a lot of metals are incorporated

inside the enzymes (iron, zinc,

selenium)

Organometallic: a

combination between an

organic structure and

metallic structure.

Example: heme (organic

structure containing iron)

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Activation transfer coenzymes -Usually participate directly in catalysis by forming a covalent bond.

Characteristics: ▪ Two groups in the coenzyme: - Forms a covalent bond (functional group) - Binds tightly to the enzyme (binding group) ▪ Dependence on the enzyme for additional specificity of substrate& additional catalytic

power. We have 13 vitamins - 4 are fat soluble (A, D, E, K) ----> they don’t work as coenzyme. - 9 are water soluble -----> all work as coenzyme (they don’t work per se except vitamin c, enter as is and work as coenzyme) - The other 8 vitamins are B’s vitamins (B1, B2, B3, B5, B6, B7, B9, B12). These 8 vitamins are get modified bound to other structure inside the body, then we name it as a coenzyme, and it helps enzyme to do their work.

This is the reactive carbon here will be dissociation of the hydrogen. The carbon will be reactive -----> it will hit the carbon in the substrate -----> the double bond will be lost ------> and the bond which connect the carboxyl group will be weak------>causing the loss of the carboxylic group from the substrate, and then there will be reformation of the double bond.

2 phosphates

The 2 phosphates

with all the

negative charge

they have are

responsible for

binding the active

site of the enzyme

(binding part)

The reactive carbon is responsible

for binding the substrate

and catalyzing the reaction

Per se = by itself

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We will find inside the active site or inside those enzymes magnesium or calcium sometimes, why? Because this magnesium with the positive charge they have it collates the pyrophosphate, it binds with the negative charges in the phosphates of that coenzyme.

which mean binding the enzyme with the coenzyme

TPP hit this carbon

causing the release of

the terminal carboxylic

group out -----> it will be

utside o 2released as CO

of the molecule

The purpose behind

having the negative

charges, the adenosine

and the pantothenic acid

is the binding to the

active site of the enzyme

and then it will be

released again .

Pantothenic acid Same as vitamin B5, which we need it to get into the structure of CoA, to work as an acyl carrier group

Acetyl ----> two

carbon units.

acetyl coA ------> two

carbon units

connected to CoA.

Acyl ----> general

name for any carbon

units above two

Carbon.

We need CoA as an acyl carrier group .

So, after the breaking down of the peripheral carbon and the carbons are

reactive, CoA comes and binds to peripheral carbon causes the stability and

then transfer it to another place releases that molecule again.

Examples of compounds that

has CoA: Acetyl CoA and

Malonyl CoA.

The full structure of the CoA:

adenosine, pyrophosphate,

pantothenic acid and

modified cysteine (This is

why it has SH).

What is the functional part of

this CoA?

It is the thiol group

(sulfhydryl group).

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✓ Wherever we here of the name carboxylase requires biotin for the reaction to go through.

Features of vitamin: 1- They are essential -----> we cannot synthesis them within our body (there is no pathway in the body to synthesize them). 2- We need them to help enzyme in doing their work ----> enzymes are already synthesized in very small amounts so coenzyme and vitamin should be in small amount. 3- They are organic in their nature.

✓ This definition is species dependent (for one of the species it is vitamin, but it is not for another one)

- Vitamin c, scientifically you should name it ascorbic acid ----> you cannot name it vitamin c except for humans, for human you can name it ascorbic acid. for dogs ----> dogs can synthesize ascorbic acid so it’s not vitamin for them it’s a ascorbic acid.

✓ What do we mean by there is no human metabolic pathway to synthesize vitamin?

This doesn’t mean that we cannot synthesis it in our body, because we have bacteria in our body. Example: biotin is synthesized by the intestinal bacteria, so it’s vitamin for us but we get it from intestinal bacteria ----> so it’s hard get a deficiency, unless the long

Vitamin: Biotin, Coenzyme: biocytin (help in

carboxylation reactions). Which is a contrary to

thiamine; the coenzyme is TPP that helps in

decarboxylation reactions.

avidin will bind the biotin and it will get outside of the body without being absorbed

Biotin comes as a coenzyme when it gets to the active site of the

enzyme, it connects itself covalently to the side chain of Lysine amino

acid, and the whole complex between biotin and lysine will be called

Biocytin.

➢ Lack of vitamins→ Lack of coenzymes→ Lack of the function of the enzymes

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antibiotic treatment which kills all the bacteria within the intestines which means there might be a deficiency in biotin, and excessive consumption of raw eggs. Cooking eggs makes denaturation, but the row eggs has a protein called avidin, which has a very high affinity to biotin.

➢ Excessive consumption of raw eggs→ Avidin will bind the biotin→ Biotin will get outside of the body without being absorbed

Vitamin: pyridoxine(B6)

Coenzyme: PLP ---> help in

transamination reaction

like:

Aspartate transaminase

Alanine transaminase

Glutamate transaminase

✓ Pyridoxine (B6) ring will bind phosphate, and it will be named pyridoxal phosphate (PLP).

✓ All transaminases for them to work there should be PLP bound to them.