Monday's Molecule #5

 
Name this molecule. You must be specific. We need the exact name and why it's important in every living cell. Comments will be blocked for 24 hours. Comments are now open. Answer tomorrow. See below for the answer.

The molecule is N-carboxyaminoimidazole ribonucleotide. Three people, "dunbar," Steve LaBonne, and "Martin S." got the right answer. N-carboxyaminoimidazole ribonucleotide is an essential intermediate in the pathway to purine synthesis in most cells. Purines are needed to make DNA and RNA. See below the fold to find out if you need this molecule ....


The relevant part of the pathway begins with aminoimidazole ribonucleotide (AIR). It is converted to N-carboxyaminoimidazole ribonucleotide in a CO2 (in the form of bicarbonate) fixing reaction that requires ATP. In the second step, the carboxylate group is shifted from the nitrogen atom to the carbon atom in the ring forming carboxyaminoimidazole ribonucleotide (CAIR). The newly added carbon atom will become C-6 of the completed purine ring.

In prokaryote, these two steps are catalyzed by separate enzymes. In eukaryotes, the two enzymes have become fused to form a single large multifunctional enzyme that can carry out both steps. In vertebrates, it is thought that a single enzyme (AIR carboxylase) can transfer bicarbonate directly to create CAIR. This conclusion is based on a single 1994 paper that studied the chicken enzyme. As far as I know it hasn't been confirmed.