What is the only macronutrient with a significant source of nitrogen?
What is the major form of nitrogen loss?
unrine as urea
When is there a positive nitrogen balance?
growing children, pregnant women, body builders
When is there a negative nitrogen balance?
protein deficiency (deficiency in one amino acid, starvation)
severe diseases (infections, wasting diseased, burns)
What three ways are the amino acid pool replenished?
digestion and hydrolysis of dietary protein
hydrolysis of body protein
de novo synthesis of non-essential amino acids
What three ways are is the amino acid pool depleted?
body protein synthesis (protein turnover)
synthesis of nitrogen containing compounds
When are body proteins degraded? (3 times)
they are damaged
they are no longer needed
amino acids are needed for energy metabolism of gluconeogenesis
What are the three proteases involved in protein turnover/degredation?
Serine protease (digestion and blood clotting)
Ubiquitin-Proteasom system (ubiquitin-tagged proteins)
Cathepsins (cysteine protease, lysosomal enzymes)
How are amino acids transported into cells of the intestine?
Secondary active Na+ dependent transport (sodium dependent transport)
What is celiac sprue?
immune mediated inflamation and damage of the mucosa in the small intestine (in response to gluten peptides; gluten intolerant)
What is Hartnup disease?
defective transporter for neutral amino acids (typtophan) in apical membanes of intestine and kidney (only clinical manifestation is deficiency of tryptophan, bacterial formation of unabsorbed tryptophan in intestine, CNS intoxication, foul smelling stools)
What is cystinuria?
deficiency of transporter for dibasic amino acids (cystine, ornithine, arginine lysine=COAL) in apical membrane of small intestine and proximal tubule
urinary exretion of cytosune and dibasic amino acids in urine
can form bladder stones
prevent by drinking lots of fluids
What two mechanisms degrade body proteins to replenish amino acids?
ubiquitin-proteasom system (degrades short-lived protein, highly ATP consuming)
autophagy-lysosome pathway (degrades long-lived proteins, less energy consuming)
What inhibits ubiquitin proteasome proteolysis?
What activates it?
Activates: starvation, immobilization, denervation, severe catabolic states
What inhibits autophagy-lysosome proteolysis?
What activates it?