Human Biochemistry, Volume 1 - Murray R. 1993

Protein and Amino Acid Metabolism
Conversion of Amino Acids into Specialized Products
Glycine

Heme Synthesis

The alpha-carbon and nitrogen atoms of Glycine are utilized in the Synthesis of the Hemoglobin porphyrin ring (see ch. 33). Glycine nitrogen serves as the source of the pyrrole ring nitrogen, while the adjacent carbon originates from the alpha-carbon of glycine. The alpha-carbon of the latter also provides the carbon atoms for the methylene bridges between the pyrrole rings.

In the "succinate-glycine cycle" (Fig. 32.1), succinyl-CoA condenses with the alpha-carbon atom of glycine to form alpha-amino-beta-ketoadipate. Succinyl-CoA is derived from The Citric Acid Cycle. Alpha-amino-beta-ketoadipate undergoes decarboxylation to yield delta-aminolevulinate—a porphyrin precursor; it is also converted into succinate and alpha-ketoglutarate (alpha-KG), which return to The Citric Acid cycle.

Disorders of heme METABOLISM will be discussed in ch. 33.

Purine Synthesis

The entire glycine molecule is incorporated into purine synthesis, providing carbon atoms 4, 5, and 7 of the purine Skeleton (see ch. 35).

Formation of Glycine Conjugates

Conjugation of glycine with cholic acid produces glycocholate. With benzoate, glycine forms hippurate (Fig. 32.2). The quantitative Assessment of the Liver's capacity to convert benzoate into hippurate was formerly used as a liver function test.

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Fig. 32.1. Succinate-glycine cycle.

Fig. 32.2. Biosynthesis of hippurate.

Creatine Synthesis

The Sarcosine moiety of creatine (N-methylglycine) is formed through the reaction of glycine with S-adenosylmethionine.