mobilization of amino acids Flashcards
what a-keto acids in metabolism do you need to know the structures of?
pyruvate, oxaloacetate, a-ketoglutaratew
what are the central pathways in metabolism?
glycolysis, gluconeogenesis, Krebs Citric Acid Cycle, Oxidative Phosporylation
what is essential for efficient metabolism?
a-keto-acids (too little, not good; too much, not good)
what do transaminases do?
catalyze two half reactions
sum: AA1+a-Keto2<=>AA2+a-Keto1
1st half reaction of enzyme-bound reactions
aldimine forms
converts to ketimine
hydrolyzes to ketoacid
2nd half reaction of enzyme-bound reactions
is reverse of 1st half reaction, using R2-KA to make R2-AA
know the structures of aldimine and ketimine for what?
enzyme bound reactions
what is true about all transamination reactions?
freely reversible; direction is solely determined by concentrations of substrates and products, ie by the sign of deltaGactual
what enzyme is used with alanine?
a-ketoglutarate
what enzyme is used with glutamate?
oxaloacetate
what enzyme is used with phenylalanine (histidine)?
transaminase
what four amino acids cannot undergo transamination?
proline, hydroxyproline, lysine, threonine
why can proline and hydroxyproline not undergo transamination
they are secondary amines
why can’t lysine undergo transamination?
if it were to undergo transamination, its keto acid product would cyclize to form a toxic non-metabolite
why can’t threonine undergo transamination?
if it were to undergo transamination, its keto acid product would dimerize into a toxic non-metabolite
glutamate dehydrogenase
major route for oxidative deamination; regenerates amino group acceptor (a-ketoglutarate) and provides ammonia, either for re-utilization or disposal as urea
GDH is located within the mitochondria (important feature of urea cycle)
glutamate dehydrogenase mechanism
1st half reaction oxidizes the amine to a protonated imine, with reduction (ie, hydride transfer) to form NADH
2nd half reaction hydrolyzes the imine to a keto acid
by storing electrons, ____&______ allows cells to manage chemical energy.
NADH and NADPH (nature’s batteries)
NADH oxidation yields energy needed to make 3 mol ATP from ADP & Pi through…
oxidative phosphorylation
GDH uses _____ to oxidatively deaminate Glutamate, forming _______, NH4 & a-ketoglutarate
NAD+, NADH
coupling of GDH and transaminases allows for…
oxidative degradation of other amino acids
when operating in the opposite direction, GDH uses _____ to make glutamate by reductive amination
NADPH
GDH uses …
NAD+ or NADPH
the direction of the GDH reaction is determined strictly by…
availability of its redox coenzyme
________ rapidly re-oxidize ______ to ______.
mitochondria, NADH, NAD+; NADH oxidation makes ATP in mitochondria
NADPH is used to make…
fatty acids, sterols, etc
high concentrations of ___,____,&_____ inhibit GDH
ATP,GTP, & NADH; reduces AA degradation & favors protein synthesis
high concentrations of _____,____&_____ activate GDH
ADP,GDP,& AAs; a-KG stimulates citric acid cycle, fueling ATP synthesis
formation of a-KG tends to increase concentration of OAA, which acts like a co-catalyst, meaning it is reformed by the time the metabolic cycle ends; more OAA means cells can make more citrate, and increased TCA cycle activity means more ATP will be made within mitochondria
_________ by GDH is part of main system for removing ammonia from amino acids/
oxidative deamination
_________________ can deaminate a few amino acids by hydrolysis and elimination reactions
mammalian
what catalyzes the hydrolysis of glutamine?
glutaminase
what catalyzes the hydrolysis of asparagine?
asparaginase
catalyzes deamination of Histidine
histidinase or histidine ammonia lyase
