Intermediate metabolite in TCA cycle are A/E

Pyruvic acid is a key substance in phase-II metabolism. 1. Principally it is formed from oxidation of glucose (glycolysis) by EM Pathway. Conversion of PA to OAA (by CO2-Fixation Reaction) Pyruvic acid can be conveed to oxaloacetate by the enzyme Pyruvate carboxylase. The enzyme requires: * 'Biotin' as a prosthetic group which brings CO2 * ATP and Mg++ * Requires 'acetyl-CoA' Acetyl-CoA does not enter into the reaction but may by combination with the enzyme maintains it in "active" conformation (+ve modifier). The generation of "acetyl-CoA" in metabolic reactions activates the enzyme and promote the formation of oxaloacetic acid (OAA) required for oxidation of acetyl-CoA in the TCA Cycle. Anaplerotic Reactions A sudden influx of Pyruvic acid (PA) or of "acetyl-CoA" to the TCA cycle might seriously deplete the supplies of OAA required for the citrate synthase reaction. Two reactions that are auxiliary to the TCA cycle operate to prevent this situation. These are known as anaplerotic (Filling up) reactions.Ref: MN Chatterjea Textbook of Medical Biochemistry, 8th Edition, Page no: 334