<prompt> Thiamine is not used in which of the following reactionsLactate to pyruvateAlphaketoglutarate to succinyl CoAGlucose to pentoseOxidative decarboxylation of alpha keto amino acids.  <response>: Ans. is a i.e., lactate to pyruvate :Lactate to pyruvate or pyruvate to lactate is a reversible reaction that is catalysed by the enzyme lactate dehydrogenase. Coenzyme is Niacin or vit. B3Thiamine is used as a coenzyme in mainly two types of reactionTransketolase reaction in HMP shunt2 Oxidative decarboxylation of alpha-keto acids eg. Pyruvate and alpha-ketoglutaratePyruvate Pyruvate dehydrogenase complex- Acetyl CoA Alpha ketoglutarate -Alpha ketoglutarate dehydrogenase complex -Suddenly CoAAlso remember the following :Coenzymes required for the following reactions:Transamination reactions-B6 Pyridoxine as pyridoxal phosphateDeamination reactions- B6 Fatty acid oxidation-B2 RiboflavinPropionyl Co A to Methyl malonyl Co A- BiotinPyruvate to oxaloacetate- BiotinAcetyl Co A to Malonyl Co A- BiotinPyruvate dehydrogenase complex- Thiamine,- B, Riboflavin - Niacin - Lipoic acidAlpha-ketoglutarate dehydrogenase complex- ThiamineB - ie alpha-ketoglutarate to succinyl Co A - Riboflavin B2- Niacin- Lipoic acidSuccinate dehydrogenase ie. Succinate to fumarate - RiboflavinB2Note: that this topic of vitamins as coenzymes is very important. A look at figure on page no. 320 of Lippincott, 2e would definitely help you. 