Liver produces ammonia?

[Flying Emu]

I was confused about a multiple choice question which appeared on one of my practice exams, the question was:

The liver is an amazing organ, with well over 300 separate functions. Which of the following is not a function normally associated with the liver?

A) Breakdown of toxic metabolites, such as alcohol.
B) Production of bile pigments
C) Production of new red blood cells
D) Releasing ammonia from the breakdown of amino acids

The answer was indeed C) but for D), does the liver really produce ammonia? I thought that was done in the digestive system.. 

[itsdanny]

I was confused about a multiple choice question which appeared on one of my practice exams, the question was:

The liver is an amazing organ, with well over 300 separate functions. Which of the following is not a function normally associated with the liver?

A) Breakdown of toxic metabolites, such as alcohol.
B) Production of bile pigments
C) Production of new red blood cells
D) Releasing ammonia from the breakdown of amino acids

The answer was indeed C) but for D), does the liver really produce ammonia? I thought that was done in the digestive system.. 

Well, nothing in the answer says anything about the "production" of ammonia. I do get what you're trying to say though, it's rather ambiguous. As most ammonia in the body forms when protein is broken down by bacteria in the intestines, hence the intestine is a major site for the production of ammonia. Now, the liver normally converts ammonia into urea, which is then eliminated in our urine. So I guess it's safe to say that they DO release ammonia, but it's not in ammonia form, but rather urea (it could also be glutamine synthesis). You shouldn't worry about it much.

[Flying Emu]

Well, nothing in the answer says anything about the "production" of ammonia. I do get what you're trying to say though, it's rather ambiguous. As most ammonia in the body forms when protein is broken down by bacteria in the intestines, hence the intestine is a major site for the production of ammonia. Now, the liver normally converts ammonia into urea, which is then eliminated in our urine. So I guess it's safe to say that they DO release ammonia, but it's not in ammonia form, but rather urea (it could also be glutamine synthesis). You shouldn't worry about it much.

I get all that, what confuses me is that D) says ammonia is released from the liver. I've got taught that the liver converts ammonia to urea so why is the liver in D) releasing ammonia?

[Russ]

C is absolutely wrong, therefore D must be right. Specifically, it does produce ammonia during amino acid catabolism (it also converts ammonia to urea, yes.)

Glutamate is acted upon in the liver, where its N-terminus is removed and replaced with a ketone group. That's the chemistry of it. So you've got a free NH3 floating around, which picks up another H and becomes NH4

Quote from my textbook

The most important ammonia-forming reaction is the oxidative deamination of glutamate by glutamate dehydrogenase in liver and other tissues. Both ammonia and aspartate [another product of glutamate catabolism] are sources of nitrogen for the synthesis of urea