The B-vitamins include thiamin (B_1), riboflavin (B_2), niacin (B_3), pantothenic acid (B_5), the B_6 complex (pyridoxal, pyridoxamine, pyridoxine), biotin (B_8 or Vitamin H), folic acid (B_9), and B_(12). Each of the B-vitamins plays a key role as either an enzymatic cofactor or metabolic constituent in many facets of intermediary metabolism. For example, about half of the propionate that reaches the ruminant liver is converted to glucose by a series of enzymatic reactions (Brockman, 1993); biotin,B_(12), niacin, pantothenic acid, and riboflavin all play essential roles in these reactions. These B-vitamins, along with the others, also play other key roles in the metabolism of carbohydrates, fats, and proteins.
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