1 1 protein & enzyme structure & function (1) amino acid & peptide 1) amino acid.

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1 protein & enzyme

structure & function (1) amino acid & peptide

1) amino acid

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A、 Biomedical importance

• 10 essential amino acids

• perform a multitude of

structure,hormone,catalitic

functions essential for life.

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• several comparatively rare

genetic disease of amino

acid catabolism

• amino acid urines

• some intracellular functions

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B 、 properties of amino acid

• the genetic code specifies 20

L--amino acids

• additional amino acid occur

in specific proteins

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• only L--amino acids occur

in protein

COOH

NH2 C H

R

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• mammals contain certain

free D-amino acid

• amino acid may have positive,

negative, or zero net charge

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(1) zwitterions

NH 3+

O -

O

R

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(2) isoelectric pH (pI)

H+ H+

R-CH-COO- R-CH-COO- R-CH-COOH

0H 0H

NH2 NH3+ NH3

+

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• the classification of amino

acid by R group

(1) hydrophobic & hydrophilic

(2) acidic & basic

(3) aromatic & aliphatic

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• the -R group determine the

properties of individual

amino acid

glycine, aliphatic R group, charged R

group, alcohol group, thioalcohol group

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• The ultraviolet absorption

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• various techniques

separate amino acids

Chromatography

electropheresis

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• functional groups dictate the

chemical reactions of amino acid

the most important reaction of

amino acids is peptide bond

formation

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2) peptides

• Hormone

• Nervous system

• antibiotics

A biomedical importance

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B L--amino acids linked by

peptide bonds form

peptide

• peptide bond

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the peptide bond has partial

double-bond character

The formation of peptide

bond

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• peptide are chain of amino

acid

• peptide can contain

unusual amino acid

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(2) The structure of protein

primary structure

three dimensional structure

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• the three dimensional

structure of a protein is

unique

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• the function of a protein

depends upon its three

dimensional structure

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• three dimensional

structure means

conformation

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• Configuration

& conformation

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1) The primary structure

• definition

• linkage bond

• importance

• example

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2) The secondary structure of

protein

• definition

• types

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a. -helix structure

• the basic characteristics

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b. -helix


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b. –pleated sheet

structure


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c. -turn


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d. Random coin


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3) Two addition structural

levels intermediate

between secondary &

tertiary structure

• Super secondary structure

• domain

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• importance

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4) the tertiary structure of

protein

• definition


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• importance

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5) the quaternary structure

of protein

• definition


subunit

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6) Bonds responsible for

higher levels of protein

structure• covalent bond

• noncovalent bond

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(3) The relationship

between structure &

functions

1) the primary structure &

function

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• the different primary

structure ,the different function

• the similar primary

structure , the similar function

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• the alteration of primary

structure of the proteins

causes molecular disease

• sickle cell anemia

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2) The relationship between

three dimensional structure

& juncture

• the special conformation,the

special function

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• allosteric effect

* definition

* significance

* instance

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(4) the classification of

protein

simple protein * conjugated protein* fibrous protein

* globular protein

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(5) The physic-chemical

properties of protein

• Macromolecular & colloid

properties

polyvalen zwitterions

(amphopathic molecules)

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• UV absorbance &

quantitative analysis

• precipitation

conception

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mechanism

methods salting out

organic reagent

heavy metal

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• denaturation

conception

factors

mechanism change of physical-

chemical properties

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characteristics

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application

the differences

between allosteric

effect & denaturation

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Enzyme

Structure & function

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1. Introduction of

enzyme

1878 Kuhne

1847 E.Bucher

1926 Summer

1982 Cech

1853 Tour, Schwann

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2. The concept of enzyme

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3. The differences between

biologic catalyst &

inorganic catalyst

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• high efficiency of

catalysis

• high specificity

• high instability

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2H2O2 2H2O+O2

Fe2+ 6 10-4

mol/mol.S

peroxidase 5 106 mol/mol.S

106-1012 倍

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4.The structure of

enzyme & catalytic

activity

• the chemical composition

of enzyme

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• simple enzyme

• holoenzyme

• apoenzyme

• cofactor

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metal ions

family of vitamin B

coenzyme

Prosthetic group

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5. The chemical structure &

catalytic function

• the active site of the enzyme

essential group

Binding group

Catalytic group

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• zymogene & activation of

zymogene

conception

method of activation

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the hypostasis &

significance

• multienzyme complex &

multifunctional enzyme

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• isoenzyme

conception

the research of isoenzyme

the damnification of

specific tissue

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lactic dehydrogenase,LDH

a.catalytic reaction

b.The molecular

structure

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MW, the type & the

number of subunits,

The physical-chemical

properties

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estimate the pathologic

changes of the tissue

• apart from the active site

the other structure

concern the catalytic

activity

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allosteric enzyme

a.concept

b.allosteric activator

allosteric inhibitor

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c. the characteristics of the

molecular structure

a) oligomers

b) binding site,catalytic site

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c) the position of the

metabolic pathway

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substrate intermediate product

Allosteric enzyme

feedback

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d) the curve of

substrate concentration

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e) Biologic significant

Modification enzyme

a) concept

b) instance

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glucogen glucogen + glucose

(Gn) (Gn-1)

phosphorylase

Active(+P)

Inactive(-p)

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6. Enzyme classification &

nomenclature

7.the mechanism of enzyme

action

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• Formation of an enzyme-

substrate complex is the

first step in enzymatic

catalysis

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transition state

Binding energy

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E+S ES ES’ E+P unstable

• decrease the activation

energies of reaction

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active molecule

active energies

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• the theory of the the

transition state

• Special catalytic group

contribute to catalysis

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9.the kinetics of enzyme-

catalyzed reaction

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• The facts affected the rate of

enzyme-catalyzed reaction

substrate

enzyme

temperature

pH

activator

inhibitor

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• how to mensurate the

rate of the enzyme-

catalyzed reaction

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• the precondition of the

research the enzyme-

catalyzed reaction

The initial velocity of

the reaction

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1) Enzyme concentration

affects the rate of enzyme-

catalyzed reaction

v=k[E]

[E]

v

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2) substrate concentration

affects the rate of enzyme-

catalyzed reaction

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• 1913 Michaelis Menten

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[S ]lower [S] vo vo=-d[S]/dt =K[S]

First order

[S] higher [S] v o vo=-d[S]/dt =K[S]

First order

[S] saturated

[S] vo

unchanged

vo=-d[S]/dt =K Zero

order

• rectangular hyperbolic plot

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• Michaelis-Menten

equation:

E + S <---> ES EP E + P

K1

K2

K3

• Michaelis-Menten constant (Km)

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vo = Vmax[S] /Km +[S]

[S] << Km, vo = Vmax[S] /Km

[S] >>Km vo = Vmax[S] / [S]

[S] =Km vo = Vmax[S] / 2[S]

= 1/2Vmax

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• the definition of Km

• the significance of Km

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Reflection of the affinity between substrate & enzyme Calculate the concentration of the substrate (which can reach the how many percentage of Vmax) or velocity of the reaction ( at the certain [S] )

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K1 K3

E + S ES E + P

K2

( K2 + K3 ) / K1 = Km

Km = K2 / K1 = [ E ] [ S ] / [ ES]

If K2 >>K3

here , Km defined as dissociation constant

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• the mensuration of the

Km & Vmax

double reciprocal plot

(lineweaver-burk plot)

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V0= Vmax [S] / ( Km + [S] )

1/v0 =Km

Vmax +

1

Vmax[S]

1

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3) enzyme activity is affected

by temperature

• optimum temperature

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v

T

optimum temperature

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4) enzyme activity is affected

by pH

• optimum pH

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5) enzyme activity is

affected by activators

• essential activators

• nonessential activators

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6) enzyme activity is

affected by inhibitors

• irreversible inhibition

specific

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acetylcholine estarase

Acetylcholine acetic acid + choline

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nonspecific

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Leurisle gas & anti

leurisle gas

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SH Cl

E + AS-CH=CHCl

SH Cl

S

E AS-CH=CHCl + 2HCl

S

+ SH

OH-CH2-CH-SH E + OH-CH2-CH-S

CH2-SH SH AS-CH=CHCL

CH2-S

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• reversible inhibition

Competitive inhibition

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characteristics

instance

K1 K3 E+S ES E+P

+ K2

I

EI

Vo Km Vm unchanged

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double reciprocal plot

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Clinical application

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angiotensin convert enzyme (ACE)

angiotension angiotensinⅠ Ⅱ

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noncompetitive inhibition

characteristics

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K1 K3 E+S ES E+P + K2 + I I

EI+S ESI

V , Km unchanged , Vm

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uncompetitive inhibition

characteristics

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K1 K3

E+S ES E+P K2 + I

ESI

V , Km , Vm

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Inhibitor

TypeBinding Site on Enzyme Kinetic effect

Competitive

Inhibitor

Specifically at the catalytic site, where it competes with substrate for binding in a dynamic equilibrium- like process. Inhibition is reversible by substrate.

Vmax is unchanged; Km, as defined by [S]

required for 1/2 maximal activity, is increased.

Noncompetitive

Inhibitor

Binds E or ES complex other than at the catalytic site. Substrate binding unaltered, but ESI complex cannot form products. Inhibition cannot be reversed by substrate.

Km appears unaltered; Vmax is decreased

proportionately to inhibitor concentration.

Uncompetitive

Inhibitor

Binds only to ES complexes at locations other than the catalytic site. Substrate binding modifies enzyme structure, making inhibitor- binding site available. Inhibition cannot be reversed by substrate.

Apparent Vmax decreased; Km, as defined by

[S] required for 1/2 maximal activity, is decreased.

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characteristics

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10 Enzyme activity detecting

& enzymatic unit

In disease diagnosis

In disease treatments

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Serum Enzyme Major Diagnostic Use

Aminotransferases

(AST) Myocardial infarction

(ALT) Viral hepatitis

Amylase Acute pancreatitis

Ceruloplasmin Hepatolenticular

degeneration (Wilson disease )

γ-glutamyl transpeptidase (γ-GT) various liver disease

LDH ,CK myocardial infarction

lipase Acute pancreatitis

Phosphatase ,acid Metastatic carcinoma of the prostate

Phosphatase, alkaline various bone disorders,

obstructive liver disease

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1.组织受损或细胞膜通透性增加

Acute pancreatitis （ amylase ）， Myocardial infarction （ LDH1 ， CPK2 ）

Viral hepatitis （ ALT ， LDH5 ）

2. 体内代谢障碍

rachitis （ AKP ）

3. 酶排泄障碍

obstructive of bile duct （ AKP ）

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4. 酶合成障碍

liver disease （ prothrombin ）

5. 肿瘤

Metastatic carcinoma of the prostate

（ Phosphatase ,acid ， ACP ）

liver cancer （ γ-glutamyl transpeptidase ， γ-GT ）

metastasis of cancer （ LDH ）

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6. 酶活性下降

toxicosis of pesticide

（ acetylcholine estarase ）

cyanide

（ cytochrome oxidase ）

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治疗应用：

助消化 ( 多酶片）

消炎（胰，糜蛋白酶）

抗凝（链激酶，尿激酶）

抗肿瘤（天冬酰胺酶）

其它（超氧歧化酶，右旋糖苷酶等）

药物酶的问题

1 1 protein & enzyme structure & function (1) amino acid & peptide 1) amino acid.

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Transcript of 1 1 protein & enzyme structure & function (1) amino acid & peptide 1) amino acid.