Serine, catabolism pyruvate from

The major pathway of serine catabolism probably is by way of its enzymatic dehydration and subsequent spontaneous deamination to yield pyruvic acid (see Fig. 2). An evidence for this is the observation of Lien and Greenberg that alanine is the major amino acid formed from serine-3-C by liver mitochondrial preparations. The alanine could be fomed from the pyruvic acid by transamination. 

A number of investigators have attempted to determine the major pathways of serine catabolism from distribution of the C Mabel of isotopic serine in glycogen and other amino acids in the intact rat (47, 4S) and in a variety of products in rat liver slices (49). The results indicated that the metabolic pathways of L-serine and D-serine are quite distinct. In other respects there is no general agreement. Koeppe and co-workers (47, 4S) determined that conversion to pyruvate is an important pathway of L-serine degradation, while an important product of unknown nature is formed as an intermediate from D-serine. Elwyn et al. (49) concluded that conversion to glycine is probably the major pathway for L-serine metabolism. 

The catabolism of glycine by way of serine and pyruvic acid is probably of little quantitative significance. This is indicated by the low degree of acetoacetate formation from glycine and serine in liver slices in contrast to the formation of acetoacetate from lactate SO). Furthermore, it is probable that serine serves as a source of glycine in the organism rather than the reverse. This is discussed under serine biosynthesis in Chapter 15. 

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