uridyl transferase

[WashMe]

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I've been trying to figure out how uridyl tranferase works in galactose metabolism. It's on p. 103 in FA 2011. Basically, it just looks like:

Galactose-1-P + UDP-glucose ----> Glucose-1-P + UDP-galactose

What's the mechanism? It just looks like a swap where the uracil diphosphate (UDP) trades its glucose for galactose, while keeping the phosphate group on whatever is not attached to UDP. Is this simple explanation good enough for our purposes? It seems weird that what you're actually doing is swapping the sugar groups on a phosphate ion (which is generally never described as the "carrier" in a reaction involving larger molecules).

Is this a reasonable understanding? Thanks 🙂

 

[WashMe]

OK, if you guys don't like that question I have another one 😀

In the urea cycle, the substrates are CO2, NH4+, and alanine (p. 105 FA 2011). In the alanine cycle, the end of the pathway in the liver is Glutamate --> urea (also p. 105). I don't see glutamate anywhere in the urea cycle...

Is it just as simple as glutamate --> aspartate (via AST), then the urea cycle goes as described in FA? If so, why didn't they just say that!!! I tried looking online for like 5 minutes and I just can't find the info.

I hate biochemistry, by the way.

 

[WashMe]

Or how about this one:

How does increased free ammonium in hyperammonemia deplete alpha-ketoglutarate? I thought you needed to have a transaminase reaction to transfer NH3 from amino acids to alpha-ketoglutarate. At high concentrations, does NH4+ just spontaneously combine with alpha-ketoglutarate? Is there another enzyme I don't know about that just puts free ammonium on other molecules?

 

[UAAWolf]

I've been trying to figure out how uridyl tranferase works in galactose metabolism. It's on p. 103 in FA 2011. Basically, it just looks like:

Galactose-1-P + UDP-glucose ----> Glucose-1-P + UDP-galactose

What's the mechanism? It just looks like a swap where the uracil diphosphate (UDP) trades its glucose for galactose, while keeping the phosphate group on whatever is not attached to UDP. Is this simple explanation good enough for our purposes? It seems weird that what you're actually doing is swapping the sugar groups on a phosphate ion (which is generally never described as the "carrier" in a reaction involving larger molecules).

Is this a reasonable understanding? Thanks 🙂

I'm just a first year....but I will tell you that the mechanism does not matter dude. Even in my biochem class now taught by an organic chemist- this does not matter.

Just know the Gal 1-p uridyl transferase deficiency is MUCH more severe than Galacotokinase deficiency....

Vignette might be like...pt has lethargy/liver/damage/******ation and also gets sick when eating lactose (breaks down to galactose)...Which enzyme deficiency?

They're probably throw 3 ****ty choices and then put in galactokinase or gal1-p U transferase.

 

[UAAWolf]

OK, if you guys don't like that question I have another one 😀

In the urea cycle, the substrates are CO2, NH4+, and alanine (p. 105 FA 2011). In the alanine cycle, the end of the pathway in the liver is Glutamate --> urea (also p. 105). I don't see glutamate anywhere in the urea cycle...

Is it just as simple as glutamate --> aspartate (via AST), then the urea cycle goes as described in FA? If so, why didn't they just say that!!! I tried looking online for like 5 minutes and I just can't find the info.

I hate biochemistry, by the way.

Glutamate is the indirect source of ammonia utilized by CPS-1, it is NOT directly in the urea cycle...your ammonia source IN THE ACTUAL CYCLE is from carbomyl phosphate and aspartate..

Realize CPS-2 in pyridmidine metabolism uses glutamine DIRECTLY unlike CPS1 which uses free nitrogen

 

[WashMe]

I'm just a first year....but I will tell you that the mechanism does not matter dude. Even in my biochem class now taught by an organic chemist- this does not matter.

Just know the Gal 1-p uridyl transferase deficiency is MUCH more severe than Galacotokinase deficiency....

Vignette might be like...pt has lethargy/liver/damage/******ation and also gets sick when eating lactose (breaks down to galactose)...Which enzyme deficiency?

They're probably throw 3 ****ty choices and then put in galactokinase or gal1-p U transferase.

Thanks for the advice 🙂 I guess the problem is that I need a reason, otherwise I won't remember it lol. I'm an excellent thinker but a terrible memorizer!

 

[UAAWolf]

Thanks for the advice 🙂 I guess the problem is that I need a reason, otherwise I won't remember it lol. I'm an excellent thinker but a terrible memorizer!

Yeah I can relate man. Anatomy was tough for me because of this...rote memory for a lot of it.


I wish I knew the mechanism (I probably know 0 mechanisms lol), but I always think of it as a "Swap".

If you are studying for biochem- I find that Kaplan does an excellent job. I hear Rapid Review Biochem is good too.

 

[bbydoc]

OK, if you guys don't like that question I have another one 😀

In the urea cycle, the substrates are CO2, NH4+, and alanine (p. 105 FA 2011). In the alanine cycle, the end of the pathway in the liver is Glutamate --> urea (also p. 105). I don't see glutamate anywhere in the urea cycle...

Is it just as simple as glutamate --> aspartate (via AST), then the urea cycle goes as described in FA? If so, why didn't they just say that!!! I tried looking online for like 5 minutes and I just can't find the info.

I hate biochemistry, by the way.

Indeed, AST takes 1 amino group of glutamate and dumps it onto oxaloacetate --> generating Aspartate which jumps into the cycle as seen on that FA diagram
but note: (its not simply glutamate --> aspartate) glutamate minus that amino group (which was dumped onto OAA) is alpha-ketogluterate which combines with incoming Alanine to again form Glutamate

 

[bbydoc]

Or how about this one:

How does increased free ammonium in hyperammonemia deplete alpha-ketoglutarate? I thought you needed to have a transaminase reaction to transfer NH3 from amino acids to alpha-ketoglutarate. At high concentrations, does NH4+ just spontaneously combine with alpha-ketoglutarate? Is there another enzyme I don't know about that just puts free ammonium on other molecules?

in 1 word, yes you are using aminotransaminases (there are 20?) which are not important enought to mention at that poin in first aid.

why you deplete alpha-ketogluterate?
you are trying to diffuse NH4 which is toxic, best way is to combine part of it (NH3) with alpha-ketogluterate --> Glutamate (still toxic as it raises pH) --> Glutamine (which does not alter pH, hence can swim in the blood in order to funnel original toxic ammonia into urea cycle in the liver)

hope i did not confuse you.

 

[WashMe]

Thanks! 🙂