1. Nitrogen balance. Digestion of proteins. Function of proteases, their regulation. Absorption of amino acids, amino acid transporters Flashcards
What is the role of nitrogenase complex?
Convert nitrogen to amonia
Give the whole equation representing the role of nitrogenase complex
(In lect)
Give the percentages of biological nitrogen fixation on earth and oceans
60% on earth
40% oceans
Definition of nitrification
the oxidation (as by bacteria) of ammonium salts to nitrites and the further oxidation of nitrites to nitrates.
Definition of denitrification
the microbial process of reducing nitrate and nitrite to gaseous forms of nitrogen, principally nitrous oxide (N2O) and nitrogen (N2)
What is the normal protein intake?
45 - 60g protein/day
What is the normal protein intake in case of pregnancy, breastfeeding?
45 - 60g/ day + 50%
What is nitrogen balance?
total daily intake equals total daily excretion 0.8 g/bw.kg/day
What is positive nitrogen balance?
Positive nitrogen balance: 1.0-1.1 g/bw.kg/day: childhood, pregnancy
What are the symptoms of Kwashiorkor?
- Decreased body weight
- Oedema (decreased albumin)
- Diarrhoea (decreased intestinal epithelial cells)
- Steatorrhoea (decreased pancreas enzyme)
- Skin atrophy
Some special aspects of the vegetarian diet
-> What is the energy content (in comparison to mixed diet)
30 - 50 cal./100g (vs. 150 - 300 cal/100 g for mixed diet)
Some special aspects of the vegetarian diet
-> What is the protein content (in comparison to mixed diet)?
Protein content: 1 - 2 g/100 g (vs 15 - 20g/100 g for mixed diet)
Some special aspects of the vegetarian diet
-> Is the protein nutritional value of vegetarian diet low or high?
Low
Some special aspects of the vegetarian diet
-> Is the digestibility of the protein low or high?
Low
Is the vegetarian diet suitable for adults? How?
Yes, it is generally enough, if the limitations are considered (legumes are low in methionine while cereals are low in lysine)
Is the vegetarian diet suitable for children and pregnancy? Why?
No, it is problematic
-> Cause low birth weight, slower growth in the first 5 years of life
What are the 9 essential AAs? (definition based on N-balance)
- Histidine (His)
- Isoleucine (Ile)
- Leucine (Leu)
- Valine (Val)
- Lysine (Lys)
- Methionine (Met)
- Threonine (Thr)
- Tryptophan (Trp)
- Phenylalanine (Phe)
What are the 3 semi-essential amino acids?
- Arginine (Arg)
- Tyrosine (Tyr)
- Cysteine (Cys)
Protein Digestion
-> Are whole proteins absorbed? Why?
No, whole proteins are not absorbed
-> Why? - Too large to pass through intact membranes
Whole proteins cannot be absorbed
-> How do our body absorb them? Is there any additional digestion?
The proteins must be digested into di- and tri- peptide or individual amino acids priot to absorption
-> Additional digestion occur in the cytosol
Are structures of protein more diverse than carbohydrates?
-> What is the consequence?
Yes, proteins structures are more diverse than carbohydrate structures
-> Proteins require broad spectrum peptidases and transporters
Protein digestion - stomach
-> What is the first step?
Chief cells secrete pepsinogen
Protein digestion - stomach
1st step: chief cells secrete pepsinogen
-> This process is stimulated by ____
Cephalic vagal input
Protein digestion stomach
1st step: chief cells secrete pepsinogen
-> What are the 3 substances that enhance this secretion?
- Acetylcholine
- cholecystokinin (CCK)
- Gastrin
Protein digestion stomach
Pepsinogen is auto-activated to pepsin at which pH?
< 4
Pepsinogen is auto-activated to which substance? (at pH < 4)
Pepsin
Protein digestion stomach
the Pepsinogen is auto-activated to which substance? (at pH < 4)
Pepsin
Protein digestion - stomach
What is the role of pepsin?
It cleaves proteins at large aliphatic or aromatic side groups (~ complete 10 - 20% of digestion)
Protein digestion stomach
At which pH that pepsin is inactivated? Why?
> 4.5; protects intestinal tissues
Protein digestion stomach
-> Protein leaves stomach as __
Mix of insoluble protein, soluble protein, peptides and amino acids
What are the 2 major enzymes that participate in digestion of proteins in intestine?
- Proteases
- Enteropeptidases
Protein digestion in the intestine
-> How are proteases produced?
They are produced as zymogens in the pancreas
Protein digestion in the intestine
-> How is the secretion of zymogens occur?
Into the intestine for secretin and cholecystokinin stimuli
Protein digestion in the intestine
-> What is the role of enteropeptidases?
It converts trypsinogen to trypsin by limited proteolysis, which in turn activates other enzymes (chymotrypsinogen, prelastase, procarboxypeptidase)
Protein digestion in the intestine
-> Enteropeptidase converts trypsinogen to trypsin by limited proteolysis, which in turn activates other enzymes which are ___ (3)
- Chymotrysinogen
- Proelastase
- Procarboxypeptidase
Where are pancreatic proteases stored?
In acinar cells as pro-enzymes (zymogens)
The role of pancreatic proteases
- Trypsinogen -> Trypsin
- Chymotrypsinogen -> chymotrypsin
- Procarboxypeptidase A & B -> Carboxypeptidase A & B
- Proelastase -> Elastase
What are the 3 amino acids that are a part of serin-proteases?
- Aspartic acid (active center)
- Histidine
- Serine (reactive)
Locations of Asp, His, Ser during activation of serin-proteases
These 3 AAs are located at very distant locations in the polypeptide chain, but are just spatially juxtaposed during activation
What are the 3 major members of the serine-proteases family?
Trypsin, chymotrypsin, elastase
What is SERPIN-s?
a broadly distributed family of protease inhibitors that use a conformational change to inhibit target enzymes.
-> another possibility to regulate protease activity
What is the role of SERPIN-s?
An ester bond is formed between COO group of the inhibitor and the Ser OH
Give a major example of an inhibitor of elastase
α1-protease inhibitor –also an inhibitor of elastase
Why is Met358 important?
It is essential for enzyme binding
How is methionine affected in smokers?
In smokers, this methionine is oxidized to methionine sulfoxide and inactivated.
=> As a result, elastases function uncontrollably, consequence: lung emphysema
How is protein digestion occur in cytosol?
- The vast majority of di- and tri- peptides are digestied into AAs by cytoplasmic peptidases
- Peptidases -> cleave N-terminal amino acids
What is the role of peptidases?
Cleaving N-terminal AAs
Protein Absorption — Amino acids
-> How many transporters of free amino acids are there in the brush border?
7
Protein Absorption — Amino acids
There are 7 transporters of free amino acids in the brush border
-> What are their mechanisms?
- Na+ - independent carriers (2)
- Proton-co transport
- Facilitated diffusion - Na+ dependent (5)
- Carriers are coupled to Na+ concentration gradient
How is protein transport occurred in basolateral membrane of the enterocyte?
The basolateral membrane of the enterocyte contains transporters which export AAs from the cell into the blood
- Diffusion
- Both Na+ depedent and indepedent carriers
Type(s) of AAs that can be absorbed into blood
Only free AAs
Protein Absorption Overview
-> Where does most protein absorption take place?
In the duodenum and jejunum
Protein Absorption Overview
-> Most AAs are absorbed into the bloodstream, but why do some AAs still remain in the enterocytes?
They are used to support the cells
Protein Absorption Overview
-> more than 99% of protein enters the bloodstream as ___
AAs
What is ubiquitinilation?
A signal for degrading denatured unfolded proteins
The ubiquitin ligases recognize different degradation signals which are ___
- Denatured, unfolded proteins
- Oxidated AA
- Modified or non-functional AA
What is an example for unbiquitinilation?
Transcriptional regulation of erithropoietin gen (EPO) by hypoxia induced factor
What are the 3 types of intracellular proteolysis? (tissue proteases)
- Lysosomal
- Proteasomal
- Autophagosomal
Tissue proteases
-> What are the 2 enzymes participating in extracellular proteases?
- Matrix metalloproteases
- Elastase
What are tissue proteases?
proteases degrading endogen proteases
What is the role of metalloproteases and cysteine Cathepsin?
Shaping dentin
What are the enzymes degrading ECM components? (teeth)
- Kollagenases
- Gelatinases
- Stromeolysine
- Enamelysine
- Cathepsin-K
Enzymes degrading ECM (teeth) derive from __
- Pulp odontoblasts
- Saliva enzymes
The organic material of dentin is 90% __
collagen
Give a major example of Zn-proteases
Matrix metalloproteinases (MMPs)
What is the role of matrix metalloproteinases?
Degrade ECM components
Matrix metalloproteinase (MMP) is synthesized as ___
an inactive proenzyme
Matrix metalloproteinases (MMPs) are activated by __
conformational change/limited proteolysis)
What are the inhibitors for matrix metalloproteinases (MMPs)?
TIMP (tissue inhibitors of metalloproteinases)
Degradation of dentin ECM by host matrix metalloproteases (MMP)
-> What will cariogenic bacteria do if they are present in the caries cavity?
They will release lactic acid and reduce the local pH
Degradation of dentin ECM by host matrix metalloproteases (MMP)
-> Degradation of dentin ECM by host matrix metalloproteases (MMP)
-> What is the consequence?
Acidic environment demineralizes the dentin matrix and induces the activation of host MMPs derived from dentin or saliva
3 steps of degradation of dentin collagen with Cathepsin - K
- Binding of catK monomers to glycosaminoglycans (GAGs) to collagen fibrils
- Dimerization of catK at the edges of gap regions
- Disintegration of collagen fibers by liberation of alpha-chain sized fragments
What is the fate of amino group in degradation of amino acids?
- Transamination
- Deamination
- Incorpration of free ammonia (Ornithine cycle)
Degradation of amino acids - Fate of amino-group
-> What happen during transamination?
Reversible exchange of the amino- and oxogroup
Degradation of amino acids - Fate of amino-group
-> What are the 2 enzymes with corresponding locations participate in the exchange of amino group?
- ALAT: Ala aminotransferase (liver)
- ASTA: Asp aminotransferase (heart and muscle)
Degradation of amino acids - Fate of amino-group
-> Characteristics of prosthetic group of the transaminases
The prosthetic group binds to Lys side chain of the enzyme
Degradation of amino acids - Fate of amino-group
-> What happen during oxidative deamination?
- Glutamate-dehydrogenase reaction
- Production of free ammonia
Degradation of amino acids - Fate of amino-group
-> What are the enzymes involving in deamination?
- a-aminogroup–oxidativedeamination
– Glu Dehydrogenase - a-amino group
– Ser(Thr) dehydratase
– His és Gly (Glycine cleavage enzyme - a-amino group oxidation with flavoproteins
– L- aminoacid oxidases (FMN, H2O, O2) - b or g amid group (deamination) – glutaminase
– asparaginase
What happen if there is a mutation in glycine cleavage enzyme?
Glycine encephalopaty
Deamination
-> What is the enzyme involving in oxidative deamination of alpha-amino group?
Glu dehydrogenase
Deamination of alpha amino group
-> What are the enzymes involving?
– Ser(Thr) dehydratase
– His és Gly (Glycine cleavage enzyme
What is the enzyme involving in alpha-amino group oxidation with flavoproteins?
- L-amino acid oxidases (FMN, H2O, O2)
- D-amino acid oxidases (FAD, H2O, O2) (bacterial AA degradation)
What are the 2 enzymes involving in deamination of beta or gamma amid group?
- Glutaminase
- Asparaginase
Free ammonia is incorporated into which cycle?
Ornithine cycle
