In 1938, pyridoxine became the first form of vitamin B6 to be isolated, and the following year it was the first to be synthesized in a laboratory. It was not until the 1940s that pyridoxal and pyridoxamine were discovered, although they contribute more to bodily vitamin B6 activity than does pyridoxine. The function of the B6 vitamins in their coenzyme form is only vaguely understood, but is, nevertheless, very important. The substance plays a role in the ability of living tissues to form and breakdown amino acids, and is involved in the synthesis of various substances, such as the neurotransmitters norepinephrine and serotonin, as well as heme, a ferrous component of hemoglobin.