Amino Acid Nitrogen Flashcards
what cells produce urea?
liver cells
ultimate fate of most of the amino acid nitrogen in the body
urea
location for urea cycle and what initiates
liver cell in fed state with amino acids coming in from a recent meal
in what ways do liver cells use carbons from amino acids?
- to make fat molecules that liver ships out in VLDLs (carbons can be delivered to adipocytes and then put into storage as stored fats)
- can be converted into glucose and liver can store as glycogen
- liver can use as fuel for ATP (through oxidation)
for nitrogens to become the N of urea, they have to enter the urea cycle as what?
ammonium ion (NH4+) and aspartate nitrogen (NH2)
fate of amino acid in fasting state
use of alanine as starting material for gluconeogenesis
- comes from muscle cells during the fasting state
- liver is using alanine’s carbons for gluconeogenesis, not nitrogens
what happens with alanine’s nitrogens in the liver’s use of it for gluconeogenesis?
what other amino acids carries N in a similar way?
gets carried from liver through the blood from muscle protein
glutamine!
when a muscle cell breaks down its muscle protein, many of the nitrogens most immediately appear as nitrogens of what?
give fate of muscle protein nitrogen
branched chain amino acids (valine, leucine, isoleucine) which are especially prevalent in building blocks of muscle protein
the Ns change from being Ns of bcaa’s to Ns of alanines and glutamines (the amino acids that muscle cells release)
Ns then beecome the Ns of ammonium ions and aspartates to become Ns of the urea cycle
(transamination rxns important in this)
describe the formation of pyridoxal phosphate (PLP)
pyridoxine ——-> pyridoxal in the oxidation of a primary alcohol catalyzed by a dehydrogenase
then a transfer of a phosphate is initiated by a kinase from an ATP
what is the function of PLP in transamination rxns ????
PLPs aldehyde carbon starts off doubly bonded to a N of a lysine side chain at a transaminase’s active site
a condensation rxn happens, resulting in a schiff base (a C=N formed by an amino group condensing with a ketone group)
explain schiff base rxns ????
- the first reactant to come into active site and push lysine’s N away and take its place is an amino acid reactant
- an isomerization happens where the double bond shifts from one side of the N to the other side
- water breaks the schiff base attachment, making a ketone and an alpha-keto acid product is created as first product
N from the first reactant is left behind in PLP’s aldehyde carbon
two major carriers of nitrogen in the blood
alanine
glutamine
give a sequence of enzyme-catalyzed reactions whereby nitrogens from muscle protein can become nitrogens of alanines
in muscle:
- bcaa + alpha-KG —————–> bcka + glutamate
enzyme: branched chain amino acid transaminase - glutamate + pyruvate —————> alpha-KG + alanine (exported)
enzyme: alanine transaminase (ALT)
give a sequence of enzyme-catalyzed reactions whereby nitrogens from muscle protein can become nitrogens of alanines
in liver:
- alanine (imported) + alpha-KG ——> pyruvate (for gluconeogenesis) + glutamate
enzyme: ALT - glutamate + OA ——> alpha-KG + aspartate (for the urea cycle)
enzyme: aspartate transaminase - glutamate + NAD(P)+ ————–> alpha-KG + NH4+ + NAD(P)H
enzyme: glutamate dehydrogenase
give a sequence of enzyme-catalyzed reactions whereby nitrogens from muscle protein can become nitrogens of glutamate
in muscle:
- bcaa (from breakdown of muscle protein) + alpha-KG ——–> beka + glutamate
enzyme: bcaa transaminase
* happens 2 times - glutamate + NAD(P)+ ——–> alpha-KG + NH4+ + NAD(P)H
enzyme: glutamate dehydrogenase - glutamate + NH4+ +ATP ———–> glutamine (exported) + ADP + Pi
enzyme: glutamine synthase
