Removal of electrons
oxidation
Gain of electrons
reduction
The process by which cells derive energy in the form of ATP from the controlled reaction of hydrogen with oxygen to form water
respiration
monooxygenases that are important for detoxification of many drugs and for the hydroxylation of steroids.
cytochrome P450 system
Enzymes involved in oxidation and reduction
oxidoreductases
4 groups of oxidoredectases
oxidases
dehydrogenases
hydroperoxidases
oxygenases
How do oxidases work?
Oxidases catalyze the removal of hydrogen from a substance using oxygen as a hydrogen acceptor
What do oxidases from as reaction products?
water or hydrogen peroxide
A widely distributed hemoprotein located in many tissues, which has the typical heme prosthetic group present in myoglobin, hemoglobin, and other cytochromes.
cytochrome oxidase
Cytochrome oxidase is poisoned by ______.
carbon monoxide
cyanide
hydrogen sulfide
Which type of oxidase contains copper?
cytochrome oxidase
Prosthetic groups contained in flavoprotein enzymes
FMN (flavin mononucleotide
FAD (flavin adenine dinucleotide)
How are FMN and FAD formed in the body?
By riboflavin
How are FMN and FAD bound to their apoenzyme proteins?
tightly bound, but not covalently bound
______ contain one or more metals as essential cofactors.
Metalloflavoproteins
Examples of flavoprotein enzymes
L-amino acid oxidase
Xanthine oxidase
Aldehyde dehydrogenase
An FMN-linked enzyme found in kidney with general specificity for the oxidative deamination of the naturally occurring L-amino acids
L-amino acid oxidase
Enzyme which contains molybdenum and plays an important role in the conversion of purine bases to uric acid
Xanthine oxidase
An FAD-linked enzyme present in mammalian livers, which contains molybdenum and non-heme iron and acts upon aldehydes and N-heterocyclic substrates
Aldehyde dehydrogenase
______ cannot use oxygen as a hydrogen acceptor, unlike oxidases.
dehydrogenases
2 main functions of dehydrogenases
Transfer of H from one substance to another in a coupled oxidation-reduction reaction (One substrate is oxidized at the expense of another.)
and
as components in the respiratory chain of electron transport from substrate to oxygen
Many dehydrogenases depend on _____ coenzymes.
Nicotinamide
How are dehydrogenases helpful?
Helps in oxidation reactions in the absence of O2 (anaerobic phase of glycolysis).
How is nicotinamide formed in the body?
From niacin
Catalyze oxi-redn reactions in the oxidative pathways of metabolism...
�Glycolysis
�Citric acid cycle
�Respiratory chain of mitochondria
NAD-linked dehydrogenases
Enzymes found in the reductive syntheses, such as the extramitochondrial pathway of fatty acid synthesis and steroid synthesis, and in the pentose phosphate pathway
NADP-linked dehydrogenases
Type of dehydrogenase concerned with electron transport in or to the respiratory chain.
riboflavin-linked dehydrogenases
___________ acts as carrier of electrons and transfers reducing equivalents directly to the respiratory chain.
-Succinate dehydrogenase
-Acyl CoA dehydrogenase
-Mitochondrial glycerol-3-phosphate dehydrogenase
NADH dehydrogenase
An intermediary carrier of electrons between acyl-CoA dehydrogenase and the respiratory chain
electron-transferring flavoprotein
(ETF)
Iron-containing hemoproteins in which the iron atom oscillates during oxidation and reduction
cytochromes
The only cytochrome that is NOT a dehydrogenase
cytochrome oxidase
Hydroperoxidases use ________ as substrate
hydrogen peroxide or an organic peroxide
Function of hydroperoxidases
protect the body against harmful peroxides
Peroxide accumulation can lead to generation of free radicals which can disrupt membranes and cause diseases including cancer and atherosclerosis
Where are peroxidases found?
milk
leukocytes
platelets
MECHANISM OF OXIDATION AND REDUCTION OF NICOTINAMIDE COENZYMES
�There is stereospecificity about position 4 of nicotinamide when it is reduced by a substrate AH2.
�One of the hydrogen atoms is removed from the substrate as a hydrogen nucleus with two electrons (hydride ion, H-) and is transferred to the 4 position, w
catalyzes an intermediate in the oxidative decarboxylation of pyruvate and alpha-ketoglutarate)
Dihydrolypoyl dehydrogenase
Which cytochromes are classified as dehydrogenases?
Cytochromes (b, c1, c)
Function of Cytochromes b, c1, and c
They carry electrons from the flavoproteins to the cytochrome oxidase.
2 categories of HYDROPEROXIDASES
Peroxidases and Catalase
Function of peroxidases
Peroxidases reduce peroxides using various electron acceptors
Peroxidase prosthetic group
protoheme
In erythrocytes and other tissues __________, containing Se as a prosthetic group catalyzes destruction of H2O2.
glutathione peroxidase
__________ uses H2O2 as electron donor and electron acceptor.
CATALASE
_________ found in many tissues including the liver are rich in oxidases and in catalase.
Peroxisomes
Catalyze synthesis or degradation of many different types of metabolites in a 2-step process.
OXYGENASES
2 subgroups of oxygenases
(1) dioxygenases
(2) monooxygenases
How do oxygenases work?
Two step process. (1) O2 bound to the active site of the enzyme and (2) bound O2 is then reduced or transferred to the substrate.
_________ incorporate both atoms of O2 into the substrate
Dioxygenases
Mixed function oxidases, hydrolases; introduce only one atom of O2 into the substrate. The other atom of O2 is reduced to H2O and an electron donor is required for this purpose
monooxygenases
A-H + O2 + Z-H2 A-OH + H2O + Z
monooxygenase
The rate of _________ of many medicinal drugs by cytochrome P450 determines the duration of their action.
detoxification
Which co-enzyme is used by an enzyme system that reduces a substrate by transferring hydrogen's from one substrate to O2?
FAD
Xanthine oxidase is used for which reaction?
Oxidation of purine
Which enzyme catalyzes this reaction....
2H2O2 ? 2H2O2 + O2
catalase
Cytochrome P450 is classified as ____________________.
monooxygenase
To decompose H2O2 to H2O, which enzyme would you use?
Hydroperoxidase
How many molecules (or moles) of CO2 are formed in one Citric acid cycle?
2
In aerobic glycolysis, Glucose is converted to what molecule?
pyruvate
Enzyme : L-Aminoacid oxidase is used for which reaction?
Oxidative deamination of amino acids
Which enzyme catalyzes this reaction...
H2O2 + AH2 ? 2H2O + A
glutathione peroxidase
Enzymes which protect aerobic organisms against oxygen toxicity
Superoxide Dismutase
How is the superoxide free radical generated?
by the transfer of a single electron to O2
True or false: Superoxide dismutase can act as both an oxidizing as well as a reducing agent.
true
How is superoxide formed?
when reduced flavins are oxidized by O2
Superoxide can oxidize ______.
cytochrome c