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. Author manuscript; available in PMC: 2019 Mar 1.
Published in final edited form as: Alzheimers Dement. 2017 Oct 19;14(3):318–329. doi: 10.1016/j.jalz.2017.09.011

Figure 1. Glycolytic intermediates are biosynthetic precursors of the non-essential amino acids, serine, glycine and alanine.

Figure 1

The three irreversible and rate-controlling steps of glycolysis are catalyzed by the enzymes, hexokinase, phosphofructokinase and pyruvate kinase, yielding intermediate metabolites that can undergo conversion to serine, glycine and alanine. The ratio of the concentrations of serine and glycine to glucose (serine+glycine:glucose) therefore reflects the net activities of the two irreversible enzymatic reactions in glycolysis that are upstream of 3-phosphoglycerate, catalyzed by hexokinase and phosphofructokinase. Similarly, the ratio of serine+glycine+alanine to glucose provides an indirect assessment of the net activity of pyruvate kinase, which catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate.