Vitamin B6 in the form of PLP and, to a lesser degree, pyridoxamine phosphate play an essential role in the interaction of amino acid, carbohydrate and fatty acid metabolism in the energy-producing TCA cycle. Over 60 enzymes are already known to depend on vitamin B6 coenzymes. Pyridoxal phosphate functions in practically all reactions involved in amino acid metabolism, including transamination, decarboxylation, deamination, and desulfhydration, as well as the cleavage or synthesis of amino acids.
Vitamin B6 has been shown to be stable to heat, acid and alkali; however, exposure to light, especially in neutral or alkaline media, is highly destructive. The free base and the commonly available hydrochloride salt are soluble in water and alcohol.
Most feedstuffs except fruits are good sources of vitamin B6. In general, muscle, liver, vegetables, whole grain cereals and their by-products and nuts are among the best sources. The vitamin B6 present in cereal grains is concentrated mainly in bran; the rest contains only small amounts. The principal source of vitamin B6 to ruminants is that obtained by microbial synthesis in the rumen.
The level of vitamin B6 contained in all feeds is affected by processing and subsequent storage. Of the several forms, pyridoxine is far more stable than either pyridoxal or pyridoxamine. Therefore, the processing losses of vitamin B6 tend to be highly variable (9% to 40%), with plant-derived foods (which contain mostly pyridoxine) losing little if any of the vitamin, and animal products (mostly pyridoxal and pyridoxamine) losing large quantities.