Figure 1. Metabolic Pathways Requiring Thiamin Pyrophosphate (TPP). As explained in the article text, TPP is critical for metabolic reactions that utilize glucose in glycolysis and the citric acid cycle. Specifically, TPP is needed for the following enzymes: transketolase in the pentose phosphate cycle, which converts ribose-5-phosphate to glyceraldehyde-3-phosphate; branched chain alpha-ketoacid dehydrogenase complex (BCKDH) in the branched amino acid catabolic pathway, which converts branch... Citric Acid Cycle, Linus Pauling, Increase Serotonin, Improve Brain Function, Muscle Protein, Magnesium Deficiency, Vitamins