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Specialty Chemistry Forums => Biochemistry and Chemical Biology Forum => Topic started by: opel65 on September 05, 2013, 01:23:54 PM

Title: Lyases of the citric acid cycle
Post by: opel65 on September 05, 2013, 01:23:54 PM

I need to name the lyases of the TCA cycle.
I know that lyases C-C, C-S and C-N bonds.

Is there something else besides fumarase that is a lyase?

Title: Re: Lyases of the citric acid cycle
Post by: Babcock_Hall on September 05, 2013, 04:06:28 PM

Lyases catalyze reactions in which something adds to a double bond or in which a double bond is formed.  Ligases  form C-C, C-S, C-O, or C-N bonds by condensation reactions.  Are you trying to find which enzymes are ligases or which are lyases?
ETA
It seems to me you must mean lyases.  Lyases can cleave C-C, C-O, C-N, and other bonds.

Title: Re: Lyases of the citric acid cycle
Post by: opel65 on September 05, 2013, 04:46:38 PM

According to my textbook:

Lyases: Catalyze cleavage of C-C, C-S, and certain C-n bonds.
Ligases: Catalyze formation of bonds between carbon and O,S,N coupled to hydrolysis to high-energy phosphate.

I need to find the lyases of the TCA cycle. I googled all the components and only fumarase was said to be a lyase

Title: Re: Lyases of the citric acid cycle
Post by: Babcock_Hall on September 05, 2013, 05:07:02 PM

Quote from: opel65 on September 05, 2013, 01:23:54 PM

I know that lyases C-C, C-S and C-N bonds.

This was the part of your message that initially threw me off, but your present definitions look OK, if a little restrictive:  other cosubstrates besides ATP are used by some ligases.  However, I suspect that you are correct with respect to fumarase being the only lyase in this cycle.

Title: Re: Lyases of the citric acid cycle
Post by: Babcock_Hall on September 06, 2013, 02:30:20 PM

Quote from: Babcock_Hall on September 05, 2013, 05:07:02 PM

However, I suspect that you are correct with respect to fumarase being the only lyase in this cycle.

I am going to have to correct myself here.  There is at least one other lyase in the TCA cycle.  The overall reaction does not give any clues to that effect, but the mechanism does.  Any thoughts on which one it is?