T E M A 12 :

-AMINOACIZII PROTEINOGENI.

PEPTIDELE.

COOH

R

COOH

R

NH2HHH2N

R CH COOH

NH2

CH COOH

R

H2N

Stereoizomeria -aminoacizilor

Formula general a -aminoacizilor

L--aminoacid D--aminoacid

Proprietile acido-bazice i structura bipolar a -aminoacizilor. Punctul izoelectric.

CH COOH

NH2

CH3

CH COOHCH3

NH3+Cl

-

CH

NH2

CH3 COONa

+HCl

+NaOH

-H2O

Clorura de alanina

Sarea de sodiu a alaninei

Alanina

H2N CH COOH

R

H2N CH

R

COO-CH COOH

R

H3N+ +H

+ +HO-

CH

R

H3N COO-+

Echilibrul ionic al -aminoacizilor n soluie

Form cationic Ion bipolar Form anionic n mediul acid (amfiion) n mediul bazic

CH COOH

NH2

CHCH3

CH3

CH COOH

NH2

CH2CH

CH3

CH3

CH COOH

NH2

CH

CH3

CH2CH3

CH COOH

NH2

CH3CH2 COOH

NH2

Clasificarea -aminoacizilor

I. -Aminoacizii alifatici monoaminomonocarboxilici

Glicin (Gli) -Alanin (Ala) acid -aminoacetic acid -aminopropionic (2-aminoetanoic) (2-aminopropanoic)

Valin (Val)* Leucin (Leu)* Acid -aminoizovalerianic Acid -aminoizocapronic (2-amino-3-metilbutanoic) (2-amino-4-metilpentanoic)

Izoleucin (Ile)* Acid-amino--metilvalerianic (2-amino-3-metilpentanoic)

II. -Aminoacizii hidroxilici (alifatici, neutri, polari)

CH COOH

NH2

CH2

OH

CH COOH

NH2

CHCH3

OH

Serin (Ser) Treonin (Tre)* Acid -amino--hidroxipropionic Acid -amino--hidroxibutiric (2-amino-3-hidroxipropanoic) (2-amino-3-hidroxibutanoic)

III. Tio--aminoacizii (mercapto--aminoacizii)

CH COOH

NH2

CH2

SH

CH COOH

NH2

CH2CH2

SCH3

Cistein (Cis) Metionin (Met)* Acid -amino--tiopropionic Acid -amino--metiltiobutiric (2-amino-3-tiopropanoic) (2-amino-4-metiltiobutanoic)

CH COOH

NH2

CH2HOOC CH COOH

NH2

CH2CH2HOOC

CH COOH

NH2

CH2CH2N

OCH COOH

NH2

CH2CH2CO

H2N

IV.-Aminoacizii monoaminodicarboxilici

Acid asparagic (Asp) Acid glutamic (Glu)

Acid -aminosuccinic Acid -aminoglutaric (2-aminobutandioic) (2-aminopentandioic)

Asparagin (Asn) Glutamin (Gln) Amida acidului asparagic Amida acidului glutamic

V. -Aminoacizii diaminomonocarboxilici

CH COOH

NH2

(CH2)3CH2

NH2

CH COOH

NH2

(CH2)3NHCH2N

NH

Lizin (Liz)* Arginin (Arg)* Acid ,-diaminocapronic Acid -amino--guanidinovalerianic (2,6-diaminohexanoic) (2-amino-5-guanidinopentanoic)

V. -Aminoacizii aromatici

CH2

NH2

COOHCH CH2

NH2

COOHCHHO

Fenilalanin (Fen)* Tirozin (Tir) Acid -amino--fenilpropionic Acid -amino--hidroxifenil propionic (2-amino-3-fenilpropanoic) (2-amino-3(p-hidroxifenil propanoic)

VII. -Aminoacizii heterociclici

N

H

CH

NH2

CH2 COOH N

N

CH

NH2

CH2

H

COOH

Triptofan (Tri)* Histidin (His)* Acid -amino--(-indolil)- Acid -amino--imidazolil-

propionic propionic

(2-amino-3-indolilpropanoic) (2-amino-3-imidazolilpropanoic)

NCOOH

HN

COOH

H

HO

NCOOH

HN

COOH

H

HO

Prolin (Pro) Hidroxiprolin Acid -pirolidin-carboxilic Acid 4-hidroxi-2-pirolidin- (2-pirolidincarboxilic) carboxilic

Iminoacizii heterociclici:

Proprietile chimice ale -aminoacizilor

H2 N CH

R

C

O

OH+ HO C2H5 H2 N CH

R

C

O

OC2H5

+ H2O(HCl)

2. Formarea srurilor complexe

CH COOH

NH2

CH3+ Cu(OH)2

C O

CH CH3H2N

O

O C

NH2CHCH3

-2H2O

2Cu

O

Alanina Dialaninat de cupru

1. Formarea esterilor

Ester etilic

3. Interaciunea -aminoacizilor cu acidul azotos (reacia de dezaminare in vitro)

H2O+N2+R CH COOH

OH

HNO2+R CH COOH

NH2

-Aminoacid -Hidroxiacid

4. Interaciunea -aminoacizilor cu aldehida formic .

R CH COOH

NH2

+ R CH COOH

N CH2+ H2O

H C

O

H

-Aminoacid Acid metileniminocarboxilic

5. Reacia de alchilare a -aminoacizilor

CH3 Cl + CH2 COOHH2N CH2 COOHHNCH3-HCl

Clorura de metil Glicin N-metilglicin

6. Reacia de acilare a -aminoacizilor.

CH3 C

O

Cl + H2N CH2 COOH CH3 C

O

NH COOHCH2

Clorur de acetil Glicin N-acetilglicin

7. Interaciunea -aminoacizilor cu fenilizotiocianat (reacia lui Edman).

+C6H5 N C

S

C

O

OHCHH2N

R

C

O

OHCH

R

C

S

NHC6H5 NH

C CH

NH

C

NC6H5

S

OR

+H+

-H2O

FenilizotiocianatProdus de aditie nucleofila

Feniltiohidantoina

FTH

Reaciile -aminoacizilor cu importan biologic.

1. Transaminarea -aminoacizilor

COOH

CH NH2

R1

COOH

C O

R2

COOH

CH NH2

R2

COOH

C O

R1

transaminazapiridoxalfosfat

+ +

N

HO

C

CH2OPO3H2

H3C

OH

-aminoacid 1 -oxoacid 2 2 -oxoacid-aminoacid 1

coenzima

Piridoxalfosfat

HOOC CH2 CH2 CH COOH

NH2

+ HOOC CH2 C COOH

OTransaminazaPiridoxalfosfat

HOOC CH2 CH2 C COOH

O

+ HOOC CH2 CH COOH

NH2

De exemplu, obinerea acidului asparagic i acidului -ceto-glutaric prin interaciunea acidului glutamic i oxalilacetic:

acidului glutamic

-ceto-glutaric

Mecanismul trancaminrii

N

C

OCH2OPO3HO

H3C

O H

H

2-

+

+ H2N CH COOH

CH2 CH2 COOH

N

CH2NH2

OCH2OPO3HO

H3C

H

+

O CH COOH

CH2 CH2 COOH+

2 -

Piridoxalfosfat Acidul glutamic

Piridoxaminfosfat Acidul 2-oxoglutaric

NCH2NH2

OCH2OPO3HO

H3C

H

++

2 -

N

C

OCH2OPO3HO

H3C

O H

H

2-

+

+

O CH COOH

CH2 COOH

CH COOH

CH2 COOH

H2N

Piridoxaminofosfat Acidul oxalilacxetic

Piridoxalfosfat Acidul asparagic

2. Dezaminarea oxidativ.

CH COOH

NH2

CH2CH2HOOC + NAD+

NH

COOHCHOOC CH2 CH2 + NADH + H+

Acid glutamic

Acid -iminoglutaric

NH

COOHCHOOC CH2 CH2

COOHCHOOC CH2 CH2

O

+ H2O

+ NH3

Acid -cetoglutaric

3. Decarboxilarea -aminoacizilor

Amina biogena-Aminoacid

CO2+piridoxalfosfatdecarboxilaza

R CH2 NH2R CH COOH

NH2

CH2 CH

OH NH2

COOH CH2 CH2

OH NH2+ CO2piridoxalfosfat

decarboxilaza

Serina Colamina

4. Hidroxilarea -aminoacizilor

CH2 CH COOH

NH2

HOCH2 CH COOH

NH2

hidroxilare

Fenilalanin-

hidroxilazaFenilalanina Tirozina

Peptidele.

H2N CH C

O

OH

CH3

+ NH CH2 C

O

OHH NH CH C

O

OH

CH(CH3)2

H+H2O-

2

H2N CH C

O

CH3

NH CH2 C

O

NH CH C

O

OH

CH(CH3)2

De exemplu, la condensarea -alaninei cu glicina i valina se obine tripeptidul alaninil-glicil-valin

Ala-Gli-Val

Structura legturii peptidice

Hidroliza peptidelor:

H2N CH C

O

R1

NH CH C

O

OH

R3

NH CH C

O

R2

H2O (H+)

H2N CH

R1

C

O

OH H2N CH

R2

C

O

OH H2N CH

R3

C

O

OH+ +

De exemplu, determinarea acidului N-terminal prin metoda Edman:

C6H5 N C

S

+ H2N CH

CH3

C

O

NH CH C

O

NH CH

H

C

O

OH

CH(CH3)2FenilizotiocianatAla Val Gli- -

C

S

NH

CHCH3

CO

C6H5 N+ CH C

O

NH CH

H

C

O

OH

CH(CH3)2

H2N

Val Gli-

FTH alanina

CH

CH3

C

O

NH CH C

O

NH CH

H

C

O

OH

CH(CH3)2

C6H5 NH C

S

NH

Sinteza chimic a peptidelor

H2N CH

CH3

C

O

OHH2N CH C

O

OHCH2OH

+ Ser - Ala

Ala - Ala

Ser - Ser

Ala - Ser

Ala Ser

1. Blocarea aminogrupei n alanin:

(CH3CO)2O + H2N CH

CH3

C

O

OHCH3 C

O

NH CH

CH3

C

O

OH+ CH3COOH

2. Activarea grupei carboxil n alanin:

3. Protejarea grupei carboxil n serin:

H2N CH C

O

OHCH2OH

+ C2H5OH H2N CH C

O

O C2H5

CH2OH

+ H2O

C6H5 CH2 O C

O

NH CH C

CH3

O

OH+ Cl C

O

O C2H5-HCl

C6H5 CH2 O C

O

NH CH C

CH3

O

O C O

O

C2H5

Etilclorformiat

4. Formarea legturii peptidice:

5. Deblocarea grupelor funcionale:

+ CH3 C

O

NH CH

CH3

C

O

O C

O

C2H5 H2N CH C

O

O C2H5

CH2OH

CH3 C

O

NH CH

CH3

C

O

CH C

O

O C2H5

CH2OH

NH + C2H5OH + CO2

CH3 C

O

NH CH

CH3

C

O

CH C

O

O C2H5

CH2OH

NHH2O CH C

O

CH2OH

NH OHCH

CH3

C

O

H2N

Ala - Ser

CH3 C

O

NH CH

CH3

C

O

CH C

O

O C 2H5

CH2OH

NHH2O C H C

O

C H2OH

NH OHCH

CH3

C

O

H2N

Ala - Ser

+ CH3COOH + C2H5OH

Dipeptide:

Carnozina

-Alanil-L-Histidina

Anserina

-Alanil-N-metil-L-Histidina

H2N CH2 CH2 C

O

NH CH COOH

CH2

N NH

H2N CH2 CH2 C

O

NH CH COOH

CH2

N NH3C

Tripeptide

H2N CH

COOH

CH2 CH2 C

O

NH CH C

O

CH2SH

NH CH2 COOH

- (-Glu-Cys-Gly) Glutation

-Glutamilcisteinglicina (-Glu-Cys-Glu)

2 Glu Cys Gly-2H

+2H

Glu Cys Gly

S

S

Glu Cys Gly

, GSH

, GSSG

Forma redus, GSL Forma oxidat, GSSG

Hormoni peptidici

H3N Cys Tyr Ile

S

S

Cys Asn Gln

Pro Leu Gly (CONH2)

1 2 3

456

7 8 9

H3N Cys Tyr Phe

S

S

Cys Asn Gln

Pro Arg Gly (CONH2)

1 2 3

456

7 8 9

Oxitocina

Vasopresina

F. Senger (1943 .)

Mr=5727

259377N65O75S6

Insulina