Antioxidants Flashcards
Reactive oxygen species
-Superoxide
-Hydrogen peroxide
-Hydroxyl radical
-singlet oxygen
-peroxynitrite
How is hydroxyl radical produced?
product of Fenton rxn catalyzed by free Fe and Cu
Singlet oxygen
Oxygen at an excited state, requiring photosensitizers and photons
Peroxynitrite
Formed by reaction of nitric oxide and superoxide
Oxidative stress
When antioxidant defenses are insufficient to neutralize all ROS
Antioxidants
Free radical scavengers
-chemicals that prevent the transfer of electron from O2 to organic molecules
-preferentially accepts unpaired electron from free radicals
-terminates free radical rxns
Antioxidant enzymes
Superoxide Dismutase
-converts superoxide produced from ETC to hydrogen peroxide
What form of superoxide dismutase are in the mitochondria vs the cytosol?
Mitochondria= Mn SOD
Cytosol= Cu and Zn SOD
Glutathione peroxidase and catalase
Converts hydrogen peroxide to H2O and O2
Note: peroxidase has selenium and catalase has Fe
Selenium
Needs to be a balance because it is both very toxic, and essential
-currently allowed up to 0.3ppm for growing pigs but there is some concern about Se pollution from manure
-narrow range for oviparous vertebrates
What forms are Selenium in?
- Se-methionine is absorbed same as methionine
- SeO4 (selenate) = resembles sulphate
Selenium absorption, excretion, and storage
Absorption: small intestines, none in rumen
Excretion: urine… controls levels
Storage: stored as SeMet and SeCys
Functions of Selenium
-component of enzyme glutathione peroxidase which is needed for the degradation of peroxides during tissue fat oxidation
-associated with Vitamin E
Se/Vit E deficiency
-White muscle disease (nutritional muscular dystrophy) in calves and lambs
-Mulberry Heart disease- pigs
-Stiff lamb disease- stiff gait and arched back
-Exudative diathesis- young chicks develop severe edema due to poor capillary integrity
Selenium toxicity in oviparous vertebrates
Se-Met and Se-Cys is incorporated in egg yolk protein, and absorbed by embryo
-can result in cataracts and spinal, skeletal, and cardiac deformities
Selenium toxicity in non-oviparous vertebrates
-Hoof problems (brittle nails)
-hair loss
Vit E functions
- Antioxidant which helps protect cell membranes from damage by radicals
-chain breaking antioxidant
-results in excretion in urine - Decreases aging process
Vit E deficiency
-fragile RBCs
-reduced fertility
Vit E storage
Adipose tissue
What is the Vit E family known as?
Tocopherols
Lipid peroxidation
-Leads to ROS
-Vit E plays a major role in stopping the lipid peroxidation
**other antioxidants can do this as well but Vit E is closer with the lipids than others
Interaction between Vit E and Selenium
- Deficiency in Vit E results in more peroxidases being formed… so need for Selenium to destroy the harmful peroxides
- Deficiency of Selenium, results in a reduced opportunity for peroxides destruction. Triggers Vit E need to prevent or cut down the formation of harmful peroxides
Vit C (ascorbic acid)
-acts as a free radical scavenger
-endogenously synthesized from glucose in animals or obtained from green/citrus plants
Functions of Vit C
-extend human life
-cofactor for several hydroxylase enzymes that synthesize or aid in collagen and carnitine
-helps with Fe absorption
Vit C deficiency and toxicity
Deficiency: scurvy in humans; uncommon in animals due to synthetic capacity
Toxicity: uncommon
