7. Copper Metabolism

Question 1

What functions is copper critical for?

Answer 1

Cellular respiration, iron homeostasis, pigment formation, neurotransmitter production, peptide biogenesis

Question 2

What gives the copper its unique redox nature?

Answer 2

Its electron structure, allows direct interaction with spin restricted dioxygen, allow enzymes which have a copper cofactor to undertake electron transfer reactions

Question 3

What are the oxidation states of copper ions?

Answer 3

+1 and +2

Question 4

Give examples of 8 different copper dependant enzymes and what they do

Answer 4

1. Ceruloplasmin: A plasma protein ferrooxidase (catalyses ox. of Fe(II)) which transports iron through the blood plasma
2. Hephaestin - intestinal ferrooxidase (transports dietary iron from enterocytes into circulatory system)
3. Superoxide Dismutase - cytosolic antioxidant defence protecting against oxidative damage
4. Extracellular superoxide dismutase
5. Amine oxidases - inactivation of bioactive amines
6. Lysyl oxidase - cross links collagen/elastin
7. Tyrosinase - produces melanin
8. Cytochrome C oxidase - complex IV in ETC

Question 5

Where does most dietary sources of copper come from? What is the average copper intake?

Answer 5

Cereals and meats (27%), and veg (17%)

1.63mg intake - 1.2mg recommended

Question 6

Which disease causes increased absorption of copper?

Answer 6

Wilson’s disease

Question 7

Which disease causes decreased absorption of copper?

Answer 7

Menke’s disease

Question 8

What other things may cause increased/decrease copper absorption?

Answer 8

Increased absorption: low copper intake, human milk, animal protein, fructose

Decreased absorption: high copper intake, cow’s milk, vegetable protein, other metals

Question 9

In which two ways may copper produce free radicals?

Answer 9

Fenton reaction: O2. + H2O2 + Cu+ –> OH. + O2 + OH- + Fe3+

Ionising (gamma) radiation: causing molecule of water to split into OH. and H.

Question 10

What is the worst free radical? What’s not so bad about it? :)

Answer 10

OH. is the most highly reactive free radical, will damage anything in it’s vicinity.

It has a small vicinity.

“Every cloud has a silver lining” - Sylvester Stallone

Question 11

What is a free radical?

Answer 11

An independent species with an unpaired electron

Question 12

What percentage of the oxygen we breathe becomes free radicals?

Answer 12

1-3%

Question 13

How does oxidative metabolism lead to production of ROS?

Answer 13

Glucose is completely oxidised to CO2 and H2O to produce ATP - but sometimes electrons leak from the ETC and react with O2 to produce O2. (then react with Cu in fenton reaction to make OH.)

Question 14

How does a copper-dependent enzyme produce free radical?

Answer 14

Cytochrome P-450 metabolises xenobiotics (foreign chemical substance) to radicals which can react with oxygen to produce superoxide (then react with Cu in fenton reaction)

Question 15

Which immune system cell produces free radicals?

Answer 15

Macrophages engulf bacteria and produce O2.- and H2O2 which then react with Cu/Fe 2+, undergo the fenton reaction and produce the highly reactive hydroxy free radicals

Question 16

What are some copper associated diseases and their causes?

Answer 16

Dietary lack of copper: Copper fever, indian childhood cirrhosis, tyrollean infantile cirrhosis

Defective copper metabolism: idiopathic copper toxicosis

Lack of bioavailable copper to brain: Alzheimers disease

Lack of caeruloplasmin (major copper/iron carrying protein in blood): Acaeruloplaminaemia

Question 17

What are the genetics, symptoms, copper levels and treatment for Wilson Disease?

Answer 17

Genetics: Autosomal recessive

Symptoms: Basal ganglia symptoms, liver disease

Copper Levels: Serum copper levels low and liver copper levels high

Treatment: Chelation

Question 18

What are the genetics, symptoms, copper levels and treatment for Menkes syndrome Disease?

Answer 18

Genetics: X-linked

Symptoms: Grey matter degeneration, abnormal/kinky hair hypothermia

Copper Levels: Serum copper low, liver copper lower

Treatment: None

Question 19

What are the genetics, symptoms, copper levels and treatment for acaeruloplasminae Disease?

Answer 19

Genetics: Autosomal recessive

Symptoms: Adult onset dementia, dystonia, diabetes, renal degeneration

Copper Levels: Serum copper low, liver copper higher

Treatment: None

Question 20

How does copper cause damage in Wilson disease?

Answer 20

Copper excess in liver causes build up of copper in neurones which leads to motor neurone degradation

Question 21

Where is copper absorbed in the body? Where is it transported form there?

Answer 21

1. Copper absorbed in stomach/duodenum
2. Transported to liver whilst bound to albumin
3. Exported to blood (from liver)
4. Bound to caeruloplasmin

Question 22

What genes does Menkes disease affect?

Answer 22

ATP7A gene mutation - this is an ATP copper transporter responsible for Cu uptake into kidney

Question 23

What genes does wilson disease affect?

Answer 23

ATP7B gene mutation - causes the liver to produce new blood vessels so excessive amount of blood/copper goes into other organs

Question 24

How does copper traverse from the apical side of the intestine to the blood?

Answer 24

1. Cu Reductase reduces Cu2+ to Cu+
2. hCTR1/DMT1 take up Cu+/Cu2+ respectively
3. Copper travels from hCTR1/hCTR2/DMT1 to ATOX1 chaperone proteins
4. ATOX1 takes copper to trans-golgi network where it forms vesicle with ATP7A
5. The ATP7A/ATOX1/Copper vesicle is transported to the membrane where it may travel into the blood

Question 25

What is the role of metallothionine?

Answer 25

Picks up any excess copper that isn’t picked up by ATOX1, high binding affinity

Question 26

How is the uptake of copper regulated in the intestine?

Answer 26

Hormones/copper/drugs can cause transcriptional changes in the cells leading to hCTR1 being taken in from surface in a vesicle (if too much copper in cell) and increased ATP7A/ATOX1 transcription which excrete copper.

Metallothionein may also act as a buffer, binding extra copper present in the cell. It is regulated by MTF-1 (transcription factor) which is activated by high zinc levels leading to greater MT transcription .

Question 27

What is the role of metallothionein?

Answer 27

Binding copper/zinc

Question 28

How many zinc/copper atoms can metallothionein bind?

Answer 28

7 zinc/copper atoms

Question 29

Give two examples of serum copper binding proteins? What do they do?

Answer 29

Albumin and macroglobulin - bind and transport copper

Question 30

What are the family of copper importers known as? What substrate do they take up? Describe their structure

Answer 30

Ctr (e.g. hCTR1, hCTR2)

Cu(I)

Small proteins containing 3 transmembrane domains, the N-terminal motif contains Met motifs

Question 31

What would a copper chaperone do? Give an example

Answer 31

Bind copper with high affinity and deliver it to a specific target protein

ATOX1 delivers copper to ATP7A and ATP7B (ATPase transporters)

Question 32

Where do the ATPase transporters/chaperones (ATP7A, ATP7B, CCS, Cox17) transport copper to?

Answer 32

ATP7A: delivers copper to copper dependent enzymes in secretory pathways

ATP7B: directs copper incorporation into caeruloplasmin (ferrooxidase- iron/copper storage protein)

CCS: Donates copper to SOD1 (cu, zn superoxide dismutase)

Cox17: delivers copper to cytochrome oxidase

Question 33

Which four proteins may the copper go to after being imported into a cell by hCtr1?

Answer 33

COX17, CCS, ATOX1/HAH1, Metallothionein pool

Question 34

Which proteins is used to eliminate excess copper?

Answer 34

Metallothioneins - scavenge/store metals

ATP7’s - eliminate excess copper (particularly ATP7B in liver)

Question 35

How does transcription of metallothionein vary with metal load? What else may it respond to?

Answer 35

Usually expressed at basal levels but increased heavy metal amount strongly induces transcription.

Will also response to oxidative stress, ionising radiation & stress

Question 36

How does copper affect MTF (metallothionein transcription factor) expression?

Answer 36

MTF1 is constitutively expressed producing MTF1. MTF1 binds close to the promoter of Metallothionein (MT) and the Ctr1B promoter.

At low copper levels, most MTF1 is exported from the nucleus so it cannot bind to MT promoters and initiate transcription. The remaining MTF1 is bound to MREs (metal response element) upstream of the Ctr1B gene. This up regulates Ctr1B - allowing more copper import into cell. Less MT is produced so less copper stored = overall copper increase in cell.

At high copper levels more MTF-1 is exported into the cell. These are able to bind to the MT promoters and initiate/upregulate MT transcription. A red thing binds the MTF-1’s present on the MRE upstream of Ctr1B and down regulates Ctr1B transcription.