Compartmentalization of pathways is one mechanism by which competing reactions in metabolism are kept separate. Vitamins are essential nutrients that are required in the diet, usually in trace amounts. Except for vitamin C, all the water soluble vitamins are components or precursors of coenzymes . Coenzymes are typically recycled in enzymatic reactions, so only low levels are required. Rather than study each of these coenzymes in detail now, we will come back to each of them as we deal with enzymes that utilize these factors.
Niacin deficiency causes pellagra in humans.