exam 2 Flashcards
non lysosomal proteases systems?
ubiquitin/ATP dependent, non-ubiquitin/ATP dependent, non-ubiquitin/ATP stimulated, multicatalytic protease (macropain), ca-dependent (calpains)
what are the enzymes involved in ubiquitination of proteins? and what happens afterwards
E1(Ub activating enzyme) binds Ub to activate it and transfers it to E2 (Ub conjugating) transfers to E3 (Ub ligase) binds to the protein. then the marked protein is recognized by Ub conjugate degrading enzyme (26S proteasome) that degrades it using 1 ATP
What is the specificity of macropain?
is a high molecular weight protease aka 20S proteasome. cleaves carboxy terminal peptide bonds of basic, hydrophobic and acidic AA
Characteristics of calpains?
degrade proteins into large fragments, more active with higher concentrations of Ca, classified based on the concentration necessary for half maximal activity: m, u, and skm (in skeletal muscle requires Ca in nm range). is inhibited by calpastatin that is stimulated by beta adrenergic agonists
3 forms of estimating protein breakdown:
non-isotopic AA release, Pulse-chase labeling (measure isotope release, cyclohexamide as inhibitor of synthesis), deuterium oxide labeling, urinary excretion of 3 methyl histidine in some species
inter organ exchange of AA in post absorptive state
muscle releases free AA, mainly Ala and Gln, Ala is taken mainly by the liver and Gln by the gut and kidneys. liver does gluconeogenesis with the absorbed aa
BCAA that are released by the muscles are mainly used by the brain to oxidize, specially Ala is used as fuel source
Ala released from muscle is used in the liver, it is first transaminated and then used in gluconeogenesis, the released glucose in circulation goes to the muscle and is used in glycolysis, the product, pyruvate is used to make alanine that will go into circulation
inter organ exchange of AA in fed (postprandial) state
Absorbed AA flow to the liver first and releases AAs, mainly BCAA, which are mainly taken by the muscles, stimulating protein synthesis, can also be used for energy and are the main amino donors to make Ala from pyruvate
what are the 5 forms of removing amino group from AA?
Transamination (E.g. Glut + oxaloacetate <-> Asp + α ketoglutarate catalyzed by glutamate transaminase), Oxidative deamination (E.G. glu dehydrogenase, AA + ½ O2 -> α keto acid + NH4), direct deamination (Histidase takes His and releases urocanate and ammonia), dehydrative deamination (Thr dehydratase), hydrolytic deamination (glutaminase or asparaginase, asn + H2O -> Asp + NH4)
most of the body ammonia comes from combination of transamination with oxidative deamination of glutamate.
what can affect the amount of free Trp in the blood?
NEFA displace it from albumin, the concentration of other large neutral AA (Phe, tyr, val, ile, leu), insulin leads to higher muscle uptake of BCAA, increasing ratio of Trp:LNAA, increasing uptake by brain
How is serotonin made?
Trp -> 5-hydroxytryptophan -> 5 hydroxytryptamine (aka serotonin), is vasoconstrictor as well. by acetylation and methylation it is ysed to produce melatonin that affects reproductive cycles
What compounds can be synthesized from Trp?
Serotonin, melatonin, niacin, skatole
characteristics of tyrosine:
can be synthesized from Phe, used to make catecholamines (dopamine, norepinephrine, epinephrine), and thyroid hormones
Some AA disorders:
Tryptophanemia, hartnup disease, tyrosinemia, alkaptonuria, albinism, parkinson’s
metabolism of aromatic AA during inflammation:
synthesis of APP is increased in the liver, these are rich in aromatic AA, but they are at low concentration in muscle, thus muscle degradation has to be increased to sustain synthesis of APP(e.g. transferrin, haptoglobin, fibrinogen)
Intestine utilization of Gln:
postprandial: absorbed by transport B, stimulates glutaminase in enterocytes
Post absorptive: most Gln comes from blood via basolateral, Na-dependent and independent, part is oxidized, part is used by glutaminase
Fasting: glutaminase is reduced, uses other substrates for energy, spares glutamine for ammoniagenesis
operative stress: gln uptake increases and uptake of glucose decreases, support need for N and C when food intake stops
sepsis: catabolic hormones such as cortisol accelerate muscle breakdown, and intestinal glutaminase is reduced to maintain Gln homeostasis
what are the two types of hepatocytes?
periportal are near the inflow of portal vein, have high glutaminase (remove NH4 to be used in ureagenesis), are the majority, low affinity for ammonia detoxification
Perivenous are near the venous outflow, have glutamine synthetase activity, capturing ammonia to make Gln, which then goes to kidneys to make ammonia, has high affinity for ammonia detoxification
how is glutamine metabolism affected during acidosis?
Gln flow is increased to the kidneys to produce NH4+ to increase proton elimination, and generate bicarbonate, so enzymes that make Gln are enhanced in the muscle and liver, that shifts Gln uptake to release, causing the liver to contribute much more Gln than usual to sustain ammoniagenesis. i.e. perivenous are more active during acidosis.
i.e. ureagenesis eliminates bicarbonate and during acidosis ammonia detoxification shifts from urea to Gln production to spare it.
how does insulin affect protein synthesis
via IRS-1 -> PI3K -> akt -> mTOR phosphorylation
how is the formation of the translation complex?
4EBP1 is phosphorylated, releasing eIF4E that binds to the 5’ cap of mRNA, associating with eIF4G, and eIF4A, thus forming the eIF4F translation complex
