Biochemistry of Amino Acids - A. Meister 1961

Intermediary Metabolism of Amino Acids
Glycine, Serine, and Sarcosine
Other Transformations of Serine

The breakdown of Serine can occur via deamination to yield pyruvic acid and ammonia; the reaction apparently proceeds through dehydration followed by the Hydrolysis of the resulting imino acid [223]:

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Such dehydration accompanied by deamination may proceed via The formation of a Schiff base with pyridoxal (p. 247). The conversion of labeled DL-serine into labeled Alanine has been observed in Liver preparations [224]. Serine dehydratase isolated from Neurospora crassa exhibits stereospecificity toward the L-isomer of serine and also deaminates L-Threonine; Pyridoxal phosphate participates as a coenzyme in this reaction [225]. D-Serine dehydratase, which is also activated by pyridoxal phosphate, has been obtained from Escherichia coli [226, 227]. On the other hand, a specific L-serine deaminase isolated from E. coli was activated by Glutathione and adenylic acid, but not by pyridoxal phosphate [228]. L-Serine dehydratase from E. coli also deaminates L-threonine; it is suggested that a single enzyme acts on both substrates.

Fig. 10. Summary scheme of Glycine, serine, and Sarcosine transformations.

Following the discovery of Transamination reactions involving serine in The Liver and Kidneys (p. 225), it became likely that ß-hydroxypyruvic acid might serve as one of the intermediates in serine METABOLISM. This keto acid or ß-phosphohydroxypyruvic acid can be formed from glyceric acid or phosphoglyceric acid, respectively. Consequently, an alternative pathway for the Synthesis and degradation of serine exists, which involves transamination reactions (see also [1085, 1086]):

It has been established that phosphoserine is present within the peptide chains of certain Proteins. Phosphoserine and its Peptides have been isolated from proteins; recently, phosphoserine was isolated in crystalline form [229–232]. The O-phosphodiester of L-serine and ethanolamine has been found in turtle Muscle [233]. Information regarding the metabolism of these compounds is sparse; it is known that some of them are sensitive to the action of Phosphatases [234].