In order to determine the major pathway of glycine degradation, you devise an experiment in which mice are fed 13C(alpha)-labeled glycine, and the livers are then isolated and radioactive intermediates detected by GC-MS. Interestingly, you find that the amino acid serine contains the most radioactivity, and that both the Calpha and Cbeta carbons of the serine residue are labeled with 13C. Explain these observations.
There are two systems at work here that are coupled together: the glycine cleavage complex and the serine hydroxymethyltransferase (SHMT).
First, glycine is broken down by the glycine-cleavage enzyme system as follows:
13C(alpha)-labeled glycine ----> CO2 ...
This solution is provided in 162 words. It discusses the glycine cleavage complex and the serine hydroxymethyltransferase, and provides a reference and attached figure to enhance understanding of the problem.