Chapter 12 BIOLOGIC OXIDATION Flashcards
defined as the 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
molecular oxygen is incorporated into a variety of substrates by enzymes designated as
Oxygenases
many drugs, pollutants, and chemical carcinogens (xenobiotics) are metabolized by enzymes of this class, known as the
cytochrome P450 system
Enzymes involved in oxidation and reduction are called
Oxidoreductases
Oxidoreductases are classified into four groups namely
- Oxidases
- Dehydrogenases
- Hydroperoxidases
- Oxygenases
- is a hemoprotein widely distributed in many tissues, having the typical heme prosthetic group present in myoglobin, hemoglobin, and other cytochromes
- is the terminal component of the chain of respiratory carriers found in mitochondria
Cytochrome oxidase
- The action of the this enzyme is blocked by carbon monoxide, cyanide, and hydrogen sulfide, and this causes poisoning by preventing cellular respiration.
- It has also been termed “cytochrome a3.”
Cytochrome oxidase
The heme a3is combined with another heme, heme a, in a single protein to form the cytochrome oxidase enzyme complex, and so it is more correctly termed ___
cytochrome aa3
Flavoprotein enzymes contain ___ as prosthetic groups.
flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD)
an enzyme found in kidney with general specificity for the oxidative deamination of the naturally occurring l-amino acids
l-amino acid oxidase
which contains molybdenum and plays an important role in the conversion of purine bases to uric acid
xanthine oxidase,
FAD-linked enzyme present in mammalian livers, which contains molybdenum and nonheme iron and acts upon aldehydes and N-heterocyclic substrates
aldehydedehydrogenase
There are a large number of enzymes in the dehydrogenase class. They perform the following two main functions:
- Transfer of hydrogen from one substrate to another in
a coupled oxidation–reduction reaction - Transfer of electrons in the respiratory chain of electron
transport from substrate to oxygen
Crossroads of metabolism, the link between anabolic and catabolic pathways
Amphibolic
– Measure of heat content of the reactants and products
– Measured in joules (J)
Enthalpy (ΔH)
True or False
Flavin groups are not generally more tightly bound to their apoenzymes than are the nicotinamide coenzymes.
False
acts as a carrier of electrons between NADH and the components of higher redox potential
NADH dehydrogenase
is an intermediary carrier of electrons between acyl-CoA dehydrogenase and the respiratory chain
electron-transferring flavoprotein (ETF)
are iron-containing hemoproteins in which the iron atom oscillates between Fe3+ and Fe2+ during oxidation and reduction
cytochromes
Two type of enzymes found both in animals and plants fall
into the hydroperoxidase category:
- peroxidases
2. catalase
play an important role in protecting the body against the harmful effects of reactive oxygen species (ROS)
Hydroperoxidases
are highly reactive oxygen-containing molecules such as peroxides which are formed during normal metabolism, but can be damaging if they accumulate
reactive oxygen species (ROS)
are found in milk and in leukocytes, platelets, and other tissues involved in eicosanoid metabolism
Peroxidases
Prosthetic group of peroxidase
protoheme
catalyzes the destruction of H2O2 and lipid hydroperoxides through the conversion of reduced glutathione to its oxidized form, protecting membrane lipids and hemoglobin against oxidation by peroxides
glutathione peroxidase
- is a hemoprotein containing four heme groups. It
can act as a peroxidase, catalyzing reactions of the type
-is also able to catalyze the breakdown of H2O2 formed by the action of oxygenases to water and oxygen
Catalase
catalyze the incorporation of oxygen into a substrate molecule in two steps:
(1) oxygen
is bound to the enzyme at the active site
(2) the bound oxygen is reduced or transferred to the substrate
Oxygenases
2 Subgroups of Oxygenates
- dioxygenases
2. monooxygenases
are an important superfamily of hemecontaining monooxygenases, and >50 such enzymes have been found in the human genome
Cytochromes P450
Transfer of a single electron to O2 generates the potentially damaging ____, which gives rise to free-radical chain reactions, amplifying its destructive effects
superoxide anion free radical
