Protein Biochemistry 2 Flashcards
5 major reactions of the urea cycle
- NH3 + CO2 + 2ATP (carbamoyl phosphate synthetase 1) –> carbamoyl phosphate
- Ornithine + carbamoyl phosphate (ornithine transcarboxylase) –> cirtrulline
- Cirtrulline + Aspartate (argininosuccinate synthase) –> argininosuccinate
- Argininosuccinate (argininosuccinase) –> arginine
- arginine (arginase) –> ornithine + urea
Location of carbamoyl phosphate synethetase I
mitochondria
Cofactors for function of carbamoyl phosphate synthetase I
arginine activates N-acetylglutamate synthase –> acetyl CoA + glutamate –> N-acetylglutamate –> allosteric activation of carbamoyl phosphate synthetase I
important reaction catalyzed by carbamoyl phosphate synthetase I
bicarb + ammonia –> carbamoyl phosphate
uses 2 of the 3 ATPs in the urea cycle
how is ammonia transported through the blood
glutamine “holds” 2 ammonia groups
synthesized from glutamate by glutamine synthetase –> takes N to liver –> NH3 release via glutaminase –> urea cycle
function of glutamate dehydrogenase
control point for protein metabolism in mitochondria. controls direction of either N removal or incorporation into amino acids
activators: ADP, GDP
inhibitors: ATP, GTP
Transport of ammonia in muscle
uses alanine (converted from pyruvate) instead of glutamine (alanine-glucose cycle) for transport to the liver. liver uses alanine to convert back to pyruvate (transamination), and glucose is remade via gluconeogenesis to be delivered back to the muscle
glucogenic amino acid breakdown
produces pyruvate or Kreb cycle intermediates
Ex: aspartate transamination –> oxaloacetate
ketogenic amino acid breakdown
no net production of glucose
Ex: lysine and leucine –> acetyle CoA
lysine and leucine are the only ketogenic amino acids
Examples of branched chain amino acids
leucine, valine, isoleucine
decarboxylation of branched chain amino acids
the three amino acids are deaminated (branched-chain aminotransferase –> a-keto acids
decarboxylated by branched-chain a-ketoacid dehydrogenase complex –> isovaleryl CoA (leucine), Isobutyryl CoA (valine), a-methyl-butyryl CoA (isoleucine)
Maple Syrup Urine Disease
deficiency of branched-chain a-ketoacid dehydrogenase complex –> buildup of a-keto acids in urine –> sweet smelling
Role of tyrosine in thyroid chemistry
used to make T4 (prohormone) –> T3 (hormone)
mechanism of thyroid hormone release
TSH –> iodide uptake and release of T4/T3
Function of thyroid peroxidase
oxidizes iodide (I-) to iodine (I2), which eventually end up bound to T3/T4
function of thyroglobulin
contains Tyr residues iodinated to form T4/T3
How is T4/T3 transported?
via thyroxin binding globulin (TBG)
Where are porphyrins produced?
liver
Reactions for porphyrin production
- Gly + succinyl CoA + (delta-aminolevulinate synthase, mitochondria) –> delta-aminolevulinic acid (ALA)
- 2xALA (delta-aminolevulinate dehydratase, cytosol) –> porphobilinogen
- Porphobilinogen –> –> –> –> protoporphyrin IV
- Protoporphyrin IX (ferrochelatase) –> heme
Porphyria
general term for diseases in porphyrin synthesis
mechanism of lead poisoning
inhibits delta-aminolevulinate dehydratase and ferrochelatase
Process of porphyrin (heme) degradation
heme –> biliverdin –> bilirubin –> bilirubin diglucuronide –> urobilinogen –> stercobilin
how is bilirubin transported in blood?
via albumin
function of ORNT1 in the urea cycle
transport ornithine in and cirtulline out of the mitochondria
