Pentose Phosphate pathway and NADPH

Question 1

What’s another name for the pentose phosphate pathway?

Answer 1

Hexose MonoPhosphate Shunt

HMP shunt

Question 2

What is the HMP shunt?

Answer 2

a branch off from the glycolytic pathway

Question 3

what purposes does HMP shunt serve?

Answer 3

• generation of NADPH

- generation of the 5-carbon sugar ribose, to be used in the synthesis of nucleotides

Question 4

Does HMP shunt produce NADPH and ribose or one or the other?

Answer 4

can produce both or one or the other depending on the need of the cell

Question 5

HMP shunt and ATP

Answer 5

NO ATP used or produced during this process

Question 6

Step 1 of HMP shunt

Answer 6

• dehydrogenation of glucose 6-P
• enzyme Glucose 6-phosphate dehydrogenase (G6PD)
• oxidative irreversible reaction
• RATE LIMITING STEP
• major point of regulation
• the flux through the pathway increases in an absorptive state

Question 7

glucose 6-phosphate dehydrogenase

Answer 7

• enzyme for the dehydrogenation of glucose 6-P

- NADP+ is required enzyme

Question 8

glucose 6-phosphate dehydrogenase inhibitor

Answer 8

NADPH is potent competitive inhibitor

Question 9

expression of glucose 6-phosphate dehydrogenase

Answer 9

up-regulated by insulin

Question 10

Step 2 of HMP shunt

Answer 10

• hydrolysis to 6-phosphogluconate
• enzyme-6-phosphogluconolactone hydrolase
• IRREVERSIBLE
• not rate limiting
• produces 1 NADPH
• oxidative

Question 11

step 3 of HMP shunt

Answer 11

oxidative decarboxylation of 6-phosphogluconate

• enzyme-6-phosphogluconate heydrogenase
• IRREVERSIBLE
• produces 1 NADPH
• oxidative

Question 12

steps 4-8 of HMP shunt

Answer 12

• nonoxidative reversible reactions
• interconversions of sugar molecules
• interconvert sugars with 3-7C-atoms
• permit synthesis of ribose 5-P used for nucleotide production
• enzyme-transketolase

Question 13

transketolase

Answer 13

• requires TPP (from thiamine)
• important in diagnosing thiamine deficiency
• done by measurment of its activity in RBCs

Question 14

structures of NADH and NADPH

Answer 14

very similar, just a small difference

-both e carriers, although not interchangeable

Question 15

NADPH functions

Answer 15

1. electron donor for the “reductive” biosynthesis of FA, cholesterol, and steroids
2. E donor for the neutralization of reactive oxygen species
3. provides reducing equivalents for cytochrome P450 monooxygenase system (for a biosynthesis of steroids and detox of xenobiotics)
4. Play role in phagocytosis
5. substrate for the synthesis of NO

Question 16

NADPH role in neutralization of ROS

Answer 16

• tripeptide: gamma-glutamylcysteinglycine (G-SH)

- Glutathion (GSH/GSSG) is the major antioxidant system

Question 17

ROS produced

Answer 17

• during aerobic metabolism
• through reactions with drugs and toxins
• when levels of antioxidants are diminished

Question 18

Monooxygenase

Answer 18

enzyme that will incorporate 1 O-atom from molecular oxygen (creating OH group) with the other being reduced to H2O

Question 19

Mitochondrial Ct P450

Answer 19

• synthesis of steroids
• inner mitochondrial membrane
• steroidogenic tissue (placenta, ovaries, testes, adrenal cortex) uses NADPH for synthesis of steroid hormones
• liver uses the same system to synthesize bile acids and vit D3
• in kidney converts vit D3 to its active form

Question 20

Microsomal systme Cyt P450

Answer 20

• membranes of smooth ER in liver cells
• detox of drugs, toxins, chemicals
• by adding O, the compound may be inactivated, made more soluble, or provide a reactive group (hydroxyl) for attachment of other compounds

Question 21

phagocytosis in WBC

Answer 21

neutrophils and mactophages (monocytes)

-generation of O free radicals aid in killing the microorganisms that the have engulfed

Question 22

The MPO system

Answer 22

combo of NADPH oxidase and myeloperoxidase are used to generate the O free radicals to aid in the destruction of microorganisms

Question 23

Chronic Granulomatous disease (CGS) caused by what?

Answer 23

rare genetic NADPH oxidase deficiency

Question 24

Chronic Granulomatous disease (CGS)

Answer 24

• persistent serve infections due to the inability to kill bacteria forming granulomas
• the granuloma is formed as a defense where the body attempts to “wall off” the collection of cells from the rest of the body

Question 25

Nitric oxide

Answer 25

- NO - synthesized from argenine, oxygen, and NADPH - very short half-life - very reactive - diffuses into cells easily since it is a gas

Question 26

NO-synthase (NOS)

Answer 26

3 enzymes product of different genes - nNOS (neural tissues) - eNOS (endothelial cells) - iNOS (inducible)

Question 27

What NOS is constitutively expressed at constant levels?

Answer 27

nNOS | eNOS

Question 28

biological activity of NO

Answer 28

- smooth muscle relaxant - used by macrophages to generate free radicals to kill microorganisms - inhibits platelet aggregation - functions as a neurotransmitter in brain

Question 29

nitroglycerin action

Answer 29

converted into NO to relax vascular smooth muscles

Question 30

Glucose 6-Phosphate dehydrogenase (G6PD) deficiency

Answer 30

- inability to detoxify oxidizing agents | - some protection against malaria

Question 31

Where is the gene for G6PD?

Answer 31

on X chromosome (defects seen mostly in males) | -in some areas 25% of males are affected

Question 32

what populations have the highest incidence of G6PD deficiency?

Answer 32

african, mediterranean, asian

Question 33

What is the incidence of G6PD among american blacks?

Answer 33

11%

Question 34

G6PD deficiency precipitating factors

Answer 34

usually only symptomatic when experiencing an oxidative stress - infection (O radicals generated by macrophages) - drugs that produce an oxidative stress - fava beans (only some deficiencies) also called favism

Question 35

clinical manifestations of G6PD deficiency

Answer 35

- almost exclusively in RBCs as an episodic hemolytic anemia in adults - neonatoal jaundice in newborns - effects on other organs/tissues are due to hemolytic anemia - shortened life span in individuals with the severe form

Question 36

Why G6PD deficiency in RBCs?

Answer 36

- BC in RBCs, the only pathway to make NADPH is via the HMP pathway - in other cell types, other pathways contribute to NADPH formation - RBCs cannot synthesize more G6PD because they have no nucleus.

Question 37

Most of the mutations that result in G6PD deficiency ...

Answer 37

affect the stability of the enzyme, which means over the life cycle of a RBC the enzyme is lost and not replaced

Question 38

characteristic of G6PD deficiency in RBCs

Answer 38

presence of Heinz bodies in RBCs

Question 39

Heinz bodies

Answer 39

precipitates of oxidized hemoglobin in RBCs

Question 40

recovery from G6PD deficiency

Answer 40

if oxidative stress is removed, usually the patient will recover as new RBCs are made