Dr.H.MOHAMMAD HANAFI, MBBS (Syd).MS.MEDICAL FACULTY UNAIR

Blog : http//mhanafi123.wordpress.com

INTRODUCTION

Carbohydrate is a staple food of Indonesian, as many others, specially

of Asian and African countries. In general, the source of carbohydrate in food derived from rice, but some are

derived from corn, sago, cassava, potatoes, sweet potatoes, and bananas.

In rice amylum is the major component. Others are minerals, vitamins, and fibers

Amylum : amylopectin and amylose

Classification of Carbohydrate• Hetero polysaccharides• Homo polysaccharides• Oligosaccharides• Disaccharides• Monosaccharide's

Digestion and absorption• Amylase pancreas (alfa amylase)

• Endopolysaccharidase : break up alfa link ( 1 4 ), except on the tip of polymers, and near the branch points.

• Result of digestion : glucose, maltose, maltotriose, iso maltose, and oligosaccharides (limit dextrins)

• Intestinal enzymes : maltase, lactase, sucrase, limit dextrase etc.

• Active absorption : glucose and galactose

Blood & guts: Putting it together for glucose transport…

Fig. 11-44

glucose

Transfer of Glucose and Other Sugars Through The Lipid Bilayer

• Because the lipid bilayer of the eucaryotic plasma membrane is impermeable for hydrophilic molecules, glucose is transported across the plasma membrane by membrane associated carrier proteins, glucose transporters. There are 2 different types of transporter proteins, which mediate the transfer of glucose and other sugars through the lipid bilayer:

• Na+-coupled carrier system (SGLT)

• The facilitative glucose transporters (GLUT)

PATH WAYS IN CARBOHYDRATE METABOLISM

Glycolysis Glycogenesis Glycogenolysis

Pyruvate oxidation

TCA Cycle

(final common pathway)

Hexose Mono-phosphate Shunt or Pentose Phosphate Pathway

Gluconeogenesis Uronic Acid pathway Fructose and Galactose

metabolism Hexosamine

GLYCOLYSIS

• Change : glucose pyruvate

glucose lactic acid

• Function : produce ATP

• Site : cytoplasm

• Aerobic glycolysis forms 7 ATP

• Anaerobic glycolysis forms 2 ATP

Pyruvate Lactate

G G 6P

HEXOKINASE GLUCOKINASE

Found in all cells except pancreas

Inhibited by ( G 6P ) Km for glucose low Catalyze the reaction Fructose (F) F 6P

• Found in liver and pancreas

• G 6P has no effect• Km for glucose high• The only enzyme for

G G 6P

G 6P F 6P

F 6P F 1,6 BP

PFK-1 Regulator enzyme

One way reaction

CH 2 O PO 32

O H

CH 2 O H

H

O H H

H HO

O6

5

4 3

2

1 CH 2 O PO 32

O H

CH 2 O PO 32

H

O H H

H HO

O6

5

4 3

2

1

A T P A D P

M g 2 +

f r u c t o s e - 6 - p h o s p h a t e f r u c t o s e - 1 , 6 - b i s p h o s p h a t e

P h o s p h o f r u c t o k i n a s e

PHOSPHO FRUCTO KINASE 1( PFK 1 )

Activators :• ADP• AMP• Pi

• NH3

• F 2,6 BP

( fructose 2,6 Bis Phosphate )

• F 6 P

Inhibitors ATP Citric acid 2,3 BP Glycerate

( in erythrocytes) Free Fatty Acid Acetyl-CoA Ketone bodies

Ketone bodies :AcetoacetateBetahydroxy ButyrateAcetone

CCCCOOH

O

OH|

CCCCOOH

CCCO

In the liver The most potent positive allosteric activator for enzyme Phosphofructokinase-1 (PFK-1), and It relieves inhibition of PFK-1 by ATP, and ↑ affinity for F 6 P Inhibit Fructose 1,6-bisphosphatase ( ↑ Km for F 1,6 BP )

UNIQUE ROLE OF 2,6 BP

F 6P F2,6 BP PFK-2

cAMP DependentProtein Kinase

Protein Protein P ( few proteins )

Phosphofructokinase-2 (PFK-2) is also a phosphatase (bifunctional

enzyme)Bifunctional enzyme has two activities:• 6-phosphofructo-2-kinase activity, decreased by phosphorylation • Fructose-2,6-bisphosphatase activity, increased by phosphorylation

fructose-6-phosphate fructose-2,6-bisphosphate

phosphatase

kinase

ATP ADP

Pi

F 1,6 BP

Gld 3P + DHAP

6

5

4

3

2

1 CH 2 O PO 32

C

C

C

C

CH 2 O PO 32

O

HO H

H O H

H O H

3

2

1

CH 2 O PO 32

C

CH 2 O H

O

C

C

CH 2 O PO 32

H O

H O H+

1

2

3

f ru c to s e -1 ,6 - b is p h o s p h a te

A ld o la s e

d ih y d ro x y a c e to n e g ly c e ra ld e h y d e -3 - p h o s p h a te p h o s p h a te

T rio s e p h o s p h a te Is o m e ra s e

In Glycolysis DHAP is converted into glyceraldehyde -3P

C

C

CH 2 O PO 32

O

C

C

CH 2 O PO 32

H O

H O H

C

C

CH 2 O PO 32

H O H

O H

H

H O H H + H + H + H +

d i h y d r o x y a c e t o n e e n e d i o l g l y c e r a l d e h y d e - p h o s p h a t e i n t e r m e d i a t e 3 - p h o s p h a t e

T r i o s e p h o s p h a t e I s o m e r a s e

C

C

CH 2 O PO 32

H O

H O H

C

C

CH 2 O PO 32

O O PO 32

H O H+ P i

+ H +

N A D + N A D H 1

2

3

2

3

1

g l y c e r a l d e h y d e - 1 , 3 - b i s p h o s p h o - 3 - p h o s p h a t e g l y c e r a t e

G l y c e r a l d e h y d e - 3 - p h o s p h a t e D e h y d r o g e n a s e

6. Glyceraldehyde-3-phosphate Dehydrogenase catalyzes:

glyceraldehyde-3-P + NAD+ + Pi

1,3-bisphosphoglycerate + NADH + H+

If oxygen available Respiratory Chain in function, by mean of Malate shuttle system oxidizes NADH in the resp. syst ; 2.5 ATP releasedNAD+ recovered, catalyzed by malate dehydrogenase

Enzyme glyceraldehyde 3P dehydrogenaserequired NAD+ in function

If R. C. not in function, NADH will reduces Pyruvate into Lactate

Exergonic oxidation of the aldehyde in glyceraldehyde-3-phosphate, to a carboxylic acid, drives formation of an acyl phosphate, a "high energy" bond (~P).

This is the only step in Glycolysis in which NAD+ is reduced to NADH.

C

C

CH 2 O PO 32

O O PO 32

H O H

C

C

CH 2 O PO 32

O O

H O H

A D P A T P

1

22

3 3

1

M g 2+

1 , 3 - b i s p h o s p h o - 3 - p h o s p h o g l y c e r a t e g l y c e r a t e

P h o s p h o g l y c e r a t e K i n a s e

This phosphate transfer is reversible (low ∆G), since

one ~P bond is cleaved & another synthesized.

The enzyme undergoes substrate-induced conformational change similar to that of Hexokinase.

C

C

CH 2 O H

O O

H O PO 32

2

3

1C

C

CH 2 O PO 32

O O

H O H2

3

1

3 - p h o s p h o g l y c e r a t e 2 - p h o s p h o g l y c e r a t e

P h o s p h o g l y c e r a t e M u t a s e

Phosphate is shifted from the OH on C3 to the OH on C2.

Fluoride

(-)

Fluoride in tooth paste inhibits oral bacterial growthF is also used in glucose determination

C

C

C H 2 O H

O O

H O P O 32

C

C

C H 2 O H

O O

O P O 32

C

C

C H 2

O O

O P O 32

O H

2

3

1

2

3

1

H

2 -p h o s p h o g ly c e r a t e e n o la t e in t e r m e d ia te p h o s p h o e n o lp y r u v a te

E n o la s e

C

C

CH 3

O O

O2

3

1A D P A T PC

C

CH 2

O O

O PO 32

2

3

1 C

C

CH 2

O O

O H2

3

1

p h o s p h o e n o l p y r u v a t e e n o l p y r u v a t e p y r u v a t e

P y r u v a t e K i n a s e

This phosphate transfer from PEP to ADP is spontaneous.

PEP has a larger ∆G of phosphate hydrolysis than ATP.

Removal of Pi from PEP yields an unstable enol, which spontaneously converts to the keto form of pyruvate.

Required inorganic cations K+ and Mg++ bind to anionic residues at the active site of Pyruvate Kinase.

P y r u v a t e K i n a s eactivity

Activators : F 1,6 BP

In the liver F 1,6 BP

able to abolish inhibition of ATP and Alanine

Inhibitors :• ATP• Free Fatty Acid• Acetyl CoA• Ketone bodies• Alanine

(in liver only)

Protein Kinase (P.K.) controls in Glycogen.

• cAMP dependent Protein Kinase activated by cAMP.

• cAMP synthesized from ATP

• enzyme adenylyl cyclase

• Glucagon activates adenylyl cyclase (through G protein)

cAMP Dependent Protein Kinase inhibits Glycolysis in two sites

1. PFK-1, with decreasing F2,6 BP.

PFK-2-P catalyzes F2,6 BP F6P + Pi.Active cAMP

Dependent P.K.converts PFK-2 PFK-2-P ( ATP ADP )

2.Inactive Pyruvate Kinase

PEP PPyruvate Kinase PK-PPyruvate Kinase is

phosphorylated by cAMP Dependent P.K.

Pyruvate Kinase phosphate

(PK-P) is inactive

If oxygen available for respiratory chain activity,Pyruvate is the end product of Glycolysis with 7 ATP as high energy phosphate.( older textbook still counting as 8 ATP).

In unaerobic Glycolysis of certain type of musclefor sprinters, lack of oxygen cause inactive respiratory chain. NADH will reduces Pyruvate, and Lactate is the final product of Glycolysis. NAD+ is ready as coenzyme for Glyceraldehyde 3P dehydrogenase

NAD+ is the target product. Lactate is the by product.Lactate is one of the substrate of gluconeogenesis, willbe taken up by the liver and changed into glucose.

C

C

CH 3

O

O

O

C

H C

CH 3

O

O H

ON A D H + H + N A D +

L a c t a t e D e h y d r o g e n a s e

p y r u v a t e l a c t a t e

Glycolysis in Erythrocyte

No mitochondriaNo Respiratory enzymesNADH reduces Pyruvate into Lactate2,3 BP Glycerate

drives oxygen dissociation of

Oxy hemoglobin to release Oxygen

inhibits PFK-1

In the tissue where oxygen required but not ATP, 1,3 BP Glycerateis converted into 2,3 BP Glycerate

Lactate release .Tissues that normally derive much of their energy from glycolysis and produce lactate include brain, gastrointestinal tract, renal medulla, retina, and skin.

Lactate production is also increased in septic shock, and many cancers also produce lactate.