test 2 lecture 23-24 Flashcards
amino acids are important source of ___ under certain physiological conditions, and in some species they are a ___ source of energy
energy
major
___ containing amino acids and short peptides respond to oxidative stress and they are the primary targets of Reactive Oxygen and Nitrogen radicals (ROS and RNS).
sulfur
____ and ____ are major anti-oxidants while S-adenosyl methionine is an
important methyl group donor. These are also targets of ROS and RNS.
Glutathione
Taurine
____ and _____ produce massive ROS in response to pathogenic infection, and they also contain efficient systems for scavenging excess ROS (reactive oxygen species).
Phagocytes
macrophages
Elimination of ____ from AA catabolism is a major health related issue.
Amino-nitrogen
In the mammals, the Amino-nitrogen is excreted as a soluble compound, ____
Urea.
In mammals, most of urea synthesis occurs in the ___ as combined efforts of ____ and ___
liver
mitochondria and cytoplasm.
Glutamate, Glutamine and Aspartic acid are the main contributors of ____ for urea synthesis
Amino-nitrogen
____ produced in mitochondria is the critical acceptor of Asp in the cytoplasm during urea synthesis.
L-Ornithine
____ have highly active and uncontrolled urea cycle and they end up synthesizing higher levels of amino acids and they degrade much higher levels of amino acids.
felines
Following oxidative deamination of Amino Acids, the remaining α-keto acids are further oxidized as potential energy source in the ____
TCA cycle.
The end point of amino acid catabolism is the carbon skeletons in the form of different α−ketoacids and free ___ from the amino nitrogen.
NH3 (or NH4 +)
Similar to the carbon chains of carbohydrates and fatty acids, the carbon skeletons of amino acids can be oxidized in ___ as source of energy.
TCA cycle
A distinctive feature of protein/amino acid catabolism is the release of amino group as free ___ which is very toxic. This problem is not encountered in the catabolic degradation of carbohydrates and fats.
NH3 or NH4+,
Part of this amino nitrogen (NH+4) is reused for amino acid biosynthesis and the other part is excreted either as ____, ___ or ___, depending on the species.
urea, uric acid, or free ammonia (NH3)
If an amino acid is essential it means ___
can not be made by body, needs to be supplemented by diet
common essential amino acids needed in cats
arginine
if an amino acid is nonessential then ___
can be made in the body
___ is synthesized by mammalian tissues, but the rate is not sufficient to meet the need during growth
arginine
___ is required in large amounts to produce cysteine if the latter is not supplied adequately by the diet
methionine
___ is needed in larger amounts to form tyrosine if the latter is not supplied adequately by the diet
Phenylananine
The definition of essential and non-essential amino acids varies depending on ___ and ___ of animals
species and age
arginine is needed more at young age, can be made in the body but not enough, needs to be supplemented
NH3 can turn into
ammonia (in fish)
urea ( in land animals)
uric acid (reptiles and birds in arid climate)
Cats and other carnivores require a high ___ diet
protein
Cats need high protein because of their long history as flesh eaters that lead into modifications of ___ and thus, nutrient metabolic pathways. This requirement is not explained by a higher amino acid requirement for protein synthesis but rather by their limited ability to control the _____.
enzyme activities
amino acid catabolic enzymes
Whatever the protein content of their diet, the activities of catabolic enzymes in cats remain constitutively high leading to a higher loss of ____.
why is this good?
amino nitrogen
helps cats break down protein into glucose
What amino acids need to be supplemented for cats
arginine, methionine and taurine.
True or False
younger cats need less protein then older cats
false
____, another Sulfur containing amino acid, can be synthesized from methionine through homocysteine pathway, provided that the diet contains sufficient methionine.
Cysteine
SAMe
S-adenosyl methionine
L-Methionine attached to adenosine (S-adenosyl methionine, SAMe) is an important ____ donor in many biochemical reactions, including synthesis of melatonin, histamine, creatine, etc.
methyl group (CH3)
will give up a methyl group and become S-adenosylhomocysteine
Homocysteine derived from this pathway (SAMe → S-adenosylhomocysteine) is also an important source of ____ in many mammalian species.
cysteine
SAMe (gives up a methyl) →
S-adenosylhomocysteine
SAMe is also used as an important nutritional supplement/____
antioxidant
____ (γ-aminosulfonic acid) is another Sulfur containing amino acid with multiple functions.
Taurine
Taurine
An important antioxidant is synthesized from Methionine or Cysteine in many animals. Taurine is found in the central nervous system, skeletal muscle and is concentrated in the brain and heart.
Animal protein is a good source of taurine, as it is not found in vegetable protein
Taurine: An important antioxidant is synthesized from ___ or ___ in many animals.
Methionine or Cysteine
Taurine is found in the ____ , skeletal muscle and is concentrated in the ___ and ___.
central nervous system
brain
and heart
___ protein is a good source of taurine, as it is not found in ___ protein.
Animal
vegetable
cysteine→ taurine steps
cysteine
cysteinesulfinate
hypotaurine
Taurine
Vegetarians with an unbalanced protein intake, and therefore deficient in methionine or cysteine have difficulty manufacturing ___
taurine
Taurine functions in electrically active tissues such as the brain and heart to help stabilize ____. It also has functions in the gallbladder, eyes, and blood vessels and appears to have some ____.
cell membranes.
antioxidant and detoxifying activity
Taurine is often used to treat ____, epileptic seizures and retinal degeneration.
ischemia- reperfusion injury
Taurine is an essential supplement in the diet of ___ and its deficiency results in a wide range of clinical signs including fetal abnormalities, delayed growth and development, central retinal degeneration and dilated cardiomyopathy.
cats
While the ability of cats to synthesize taurine from ___ and ___ is very limited,
they also use taurine in bile acid synthesis. This is the reason for supplementing the cat food
with Taurin (discussed later in Liver function).
methionine
cysteine
Glutathione (GSH) is a ____
tripeptide (γ-Glutamyl-Cysteinyl-Glycine)
Glutathione (GSH) is a tripeptide (γ-Glu-Cys-Gly) in which the γ-carboxyl group of Glu is involved in peptide bond formation with the α-amino group of Cys. This is a powerful ___ that can scavenge reactive oxygen species, peroxides and reactive radicals
reductant
Oxidized GSH
GSSG (glutathione disulfide)
dimer of 2 GSH bonded by the S in a disulfide bond
O2-.
superoxide anion
H2O2
hydrogen peroxide
OH.
hydroxyl radical
NO
Nitric Oxide
O2 (free electrons) →
superoxide anion (O2-.)
super oxide anion (SOD)→
SOD (superoxide dysmutase)
H2O2 (hydrogen peroxide)
H2O2 can turn into 3 things:
(catalase) H20
(MPO) HOCl
.OH-
superoxide anion + nitric oxide →
ONOO-
____reduce or prevent the formation of free radical species
Primary Antioxidants
antioxidants work by ___
converting the existing free radicals to less harmful molecules
Free radicals contain electron deficient reactive groups or compounds that can be neutralized by combining with other ____
electron rich molecules.
Superoxide dismutase (SOD) converts ____ to hydrogen peroxide (H2O2) which is also harmful
superoxide (O2.-)
Glutathione peroxidase (GPx) converts___ and lipid peroxides to harmless molecules.
H2O2
___converts H2O2 and lipid peroxides to harmless molecules.
Glutathione peroxidase (GPx)
___ regenerates reduced GSH from oxidized or dimerized form containing a disulfide bond
Glutathione reductase
GSSG (___) → GSH
Glutathione reductase
(NADPH + H+) → NADP +
Physiological compounds that are anti-oxidants:
N-acetyl cysteine, GSH, SAMe, Taurine, Vitamin C, Vitamin E, CoQ, etc.
ROS
Reactive oxygen species (ROS) are produced as part of normal respiration, and functions of other oxidoreductases in different pathways.
They are electron deficient molecules which covalently bind to compounds with electron rich groups (proteins, amino acids, nucleic acids, and even lipids) and damage the molecules.
___ is the most potent and abundant antioxidant in mammals and the levels of reduced ___ is direct measure of the health status and resistance to infection and drug induced injury.
Glutahione (GSH)
GSH
GSH (H2O2) →
glytathione (hydrogen perioxide) → glutathione disulfide and 2H2O
GSSG
Taurine is the only known antioxidant that can detoxify ___
HOCl
Hypochlorous acid
Taurine + HOCl →
N-Chlorotaurine + H2O
Two parallel pathways exist for neutralizing the reactive O2 species (ROS).
Explain Catalase pathway
superoxide radicals (SOD- superoxide dismutase) → H2O2
2 H2O2 (catalase)→ 2H2O + O2
Two parallel pathways exist for neutralizing the reactive O2 species (ROS).
Explain Glutathione pathway
superoxide radicals (SOD- superoxide dismutase) → H2O2
2 GSH +H2O2 (glutathione peroxidase) → GSSG + 2 H2O
GSSG + NADPH + H+(glutathione reductase) → 2 GSH + NADP+
Formation of OH.radicals
GSSG
glutathione disulfide (oxidized GSH)
Cancer, DM, obesity, inflammation, neurodegenerative disease, arthritis, rental and intestinal disorders are conditions associated with ____
increase ROS production
ROS= reactive oxygen species
H2O2 are broken in to ___ by catalase and glutathione peroxidase
water
and other stuff
Three most common places to produce ROS
Endoplasmic reticulum
mitochondria (Electron transport chain)
plasma membrane ( NADPH oxidoreductase NOX)
Generally, reactive oxygen radicals (with electron deficiency) are converted to hydrogen
peroxide by the action of ___
superoxide dismutase
(SOD)
Hydrogen peroxide (and also lipid peroxides) is detoxified by \_\_\_ in presence of GSH.
glutathione peroxidase
NADPH and ____ are needed to maintain a steady pool of reduced GSH, which undergoes reversible oxidation (GSSG) in response to oxidative stress.
glutathione reductase
A large fraction of cellular NADPH pool, particularly in red blood cells, phagocytes and
macrophages is used for maintaining the reduced GSH pool. Scavenging of reactive oxygen species, peroxides, and reactive chemicals/radicals requires ____.
glutathione peroxidase enzyme.
In most land mammals the amino nitrogen generated from amino acid degradation is excreted as ___ through urine.
urea
Urea synthesis occurs only in the ___ in a highly coordinated way to prevent release of free NH3 in the blood plasma.
liver
During production of urea
The amino nitrogen is shuttled between different α-keto acids (carbon skeletons of amino acids) as part of a strategy to maintain Nitrogen balance of the body. __ and __ are the final donors of excess amino nitrogen for urea synthesis in the liver. Thus, excess amino nitrogen from all different tissues of the body is brought to the liver for final disposal as urea.
Asp (aspartic acid) (apartate)
Glu (Glutamic acid) (glutamate/glutamine)
excess amino nitrogen from all different tissues of the body is brought to the ___ for final disposal as urea.
liver
Nitrogen containing components of normal urine
Urea (86%)
Creatinine (4.5%)
ammonium (2.8%)
uric acid (1.7%)
other (5%)
Since free NH3 is highly toxic to different tissues, amino nitrogen from different tissues is transported to the liver through specific carriers, namely __ and __
Alanine and Glutamine.
Strategies for transporting excess amino nitrogen to the liver:
Skeletal muscle, a major generator of amino nitrogen, uses Alanine and Glutamine to carry amino nitrogen to the liver
the alpha-keto acids for both Alanine and Glutamine are produced as biproducts of glycolysis and or TCA cycle. (except in RBC)
Amino nitrogen generated in most other tissues is brought to the liver through an indirect and long route involving the intestine.
Skeletal muscle, a major generator of amino nitrogen, uses ___ to carry amino nitrogen to the liver
Alanine and Glutamine
the alpha-keto acids for both Alanine and Glutamine are produced as biproducts of ___ or ____ (except in RBC)
glycolysis and or TCA cycle.
Amino transferases represent a family of enzymes involved in shuttling from ___ to the other.
one amino acid back bone (α-keto acid)
Amino transferases occur in all tissues and are regarded as ___, essential for nitrogen economy, transport and excretion.
house keeping enzymes,
L-Glutamate + pyruvate
glutamate + oxaloacetate (GOT and PLP) →
aspartate + alpha-ketoglutartate
muscle protein breakdown:
Amino nitrogen from other tissues to the liver is carried through ___
glutamine
Glutamine is used as the vehicle for transporting ___ from different tissues such as brain, non-skeletal muscle, adipose, pancreas, etc. to the liver via ___.
amino nitrogen
the intestine
Some ___ is also used in kidney cortex for supporting gluconeogenesis, and its amino nitrogen is excreted through urine as NH4+.
glutamine
___ serves as a carrier of ammonia equivalents and of the carbon skeleton of pyruvate from muscle to liver. The ammonia is excreted and the pyruvate is used to produce ___, which is returned to the muscle
Alanine
glucose
pathway of glutamine
___ is the major carrier of excess amino nitrogen from other tissues to the liver
glutamine
the Nitrogen of urea come from
glutamate or glutamine in the mitrochondria
and
aspartate
Urea Cycle
in high energy conditions within the body, ___ is favored over ___ for the Urea Cycle
glutamine
Glutamate
(high ATP inhibits glutamate dehydrogenase)
glutamate dehydrogenase is used in ___ cycle to convert ___ to ____ and ___. What inhibits this enzyme
Glutamate
alpha- Ketoglutarate and NH+4
GTP (high energy)
Ac-CoA
Glutamine (___)→ Glutamate and Urea
glutaminase (liver mitochondria)
___ is the major pathway for the elimination of amino-nitrogen in most land mammals.
Urea cycle
This ____ takes place by a cooperative effort between the mitochondrial and cytosolic compartments in the liver (exclusively in the liver)
urea cycle
In the urea cycle, the rate limiting first reaction of the pathway starts in mitochondria by the action of mitochondrial ____, forming carbamoyl phosphate.
carbamoyl phosphate synthetase
In the urea cycle, ___or ____ are donors of NH4+ for this first reaction.
Glutamate or glutamine
in the urea cycle, ___ formed in mitochondria is transported to the cytoplasm where it is converted to Arginine by the addition of one more amino group from Aspartic acid.
Citrulline
Aspartic acid is clipped to yield ___ and ____ by enzyme arginase in the cytoplasm. ____ formed in this step is transported to mitochondria where it continues the cycle by accepting carbamoyl phosphate
urea
ornithine
Ornithine
in the urea cycle, The first ___ reactions of the pathway occur inside mitochondria and the last ___ reactions occur in the cytoplasm.
2, 4
Cats and other carnivores have constitutively active and high urea cycle activity. These animals therefore degrade amino acids and excrete amino nitrogen as urea at a higher level than omnivores and herbivores, irrespective of whether they consume diet low or high in ___
proteins.
In other mammalian species including humans and dogs, the urea cycle enzymes are highly regulated—they are induced immediately after a meal rich in ____ and brought back to basal level when the amino acid pool in the tissues goes down. In other words, in the cat the urea cycle is unregulated while in other animals it is highly regulated by dietary conditions.
amino acids (proteins)
urea cycle
NH4+(Carbamoyl phosphate synthetase I (mitochondria))→ carbomoyl phosphate
carbomoyl phosphate + ornithine( Ornithine carbamoyl transferase (mitochondria) )→ citrulline
citrulline( Arginosuccinate synthetase (cytosol) ) → argininosuccinate
argininosuccinate (Arginosuccinate lyase (cytosol))→ Arginine and Fumarate
Arginine ( Arginase (cytosol))→ ornithine and Urea
____ is activated at high energy charge and high amino acid load conditions, but ____ is used at low energy charge and high amino acid load conditions. The latter directly fuels the TCA cycle by generating α-ketoglutarate, which is component of the TCA cycle.
Glutaminase
glutamate dehydrogenase
Glutamate dehydrogenase
This mitochondrial enzyme has a dual role of both trapping free NH3 and generating free NH3 for urea synthesis in liver mitochondria.
Under intra-mitochondrial conditions of high glutamate concentrations of 10-3 M, high NAD+:NADH ratio and low energy charge, the forward reaction (oxidative deamination of Glutamate), which liberates free ammonia is favored.
ATP/GTP and NADH (NADPH) are allosteric inhibitors. ADP and NAD+ are activators.
The enzyme is also negatively modulated by acetylation at Lys residues. Ammonia generated is used for urea synthesis.
Important point of connection between urea cycle and TCA cycle since α-ketoglutarate generated here can be directly used for energy production through TCA cycle.
___ converts glutamine to glutamate by simple hydrolysis of the amide bond, thus liberating NH4+ and glutamate.
Glutaminase:
It occurs primarily in the small intestine, kidney and liver mitochondria.
The NH4+ liberated in the kidney is excreted through urine,
in liver mitochondria is used in urea synthesis.
in the intestine is metabolized by the intestinal micro organisms or transported to the liver through portal blood supply, where it is trapped as Glutamine
Hyper-ammonemia in cats:
A single meal low or lacking in Arg induces hyperammonemia (elevated blood ammonium level) in cats.
It is therefore imperative to supplement the cat diet with Arg.
constitutively high urea cycle activity and also inability to synthesize adequate level of L-ornithine from an alternate pathway starting from Glutamate.
Most mammals including dogs and humans can synthesize L-ornithine from glutamate in amounts that is needed to keep the urea cycle running efficiently. In cats this alternate pathway is relatively silent because of defective or the low activity of ornithine amino transfease, an enzyme that converts glutamate semialdehyde to L-ornithine. Thus the cats rely nearly exclusively on Arg to generate sufficient L-0rnithine by the action of arginase.
In cats, Arg supplementation include cats constitutively high urea cycle activity and also inability to synthesize adequate level of ___ from an alternate pathway starting from Glutamate.
L-ornithine
In cats this alternate pathway is relatively silent because of defective or the low activity of ____, an enzyme that converts glutamate semialdehyde to L-ornithine. Thus the cats rely nearly exclusively on Arg to generate sufficient L-ornithine by the action of arginase.
ornithine amino transfease
Two sources of L-ornithine for urea biosynthesis
urea cycle: arginine (urginase)→ L-ornithine and urea
Glutamate → pyrroline-5-carboxylate→ glutamate semialdehyde → L- ornithine
(dont need to know steps)
(this pathway is silent in felines)
ketogenic amino acids make ___
acetyl CoA or Acetoacetyl CoA
or for fatty acid synthesis
Glucogenic amino acids are used for ___
steps of TCA cycle
fate of carbon skeletons of amino acids
Glucogenic- Many of the α-ketoacids from amino acid degradation (Pyruvate, a-ketoglutarate, oxaloacetate, etc) are directly used in TCA cycle as source of energy. Others are converted to one of the five TCA cycle intermediates and used for generating energy.
Ketogenic- In some cases they are converted to Acetyl CoA or aceto- acetyl CoA and used in TCA cycle.
