Coenzyme
While all enzymes belong to the protein family, many of them are unable to participate in a catalytic reaction until they link with a nonprotein component, or coenzyme. This can be a metal ion-- copper, iron, or manganese, for instance--or a moderately-sized molecule called a prosthetic group. Quite often, though, coenzymes are composed wholly or partially of vitamins. Although some enzymes are attached very tightly to their coenzymes, others can be easily parted. In either case, the parting almost always deactivates both partners.
The first coenzyme was discovered by English biochemist Sir Arthur Harden. Toward the end of the nineteenth century, Harden began an intense study of the fermentation process, particularly alcoholic fermentation. Inspired by Eduard Buchner--who, in 1897 had discovered an active enzyme in yeast juice that he had named zymase--Harden used an extract of yeast in most of his studies.
In 1904, Harden, while working with William J. Young, made a surprising discovery. He'd already learned that boiling yeast juice appeared to destroy all its enzyme activity. However, he found that, when he added some of the boiled and presumably useless yeast juice to an active batch, the active yeast juice suddenly showed an increased capacity to ferment glucose. Some active principle, he reasoned, must have survived the boiling. To solve the chemical mystery, Harden used a filtration process called dialysis. He placed another batch of yeast juice in a semipermeable bag, then left the bag in a container of pure water. Before long, the juice's smaller molecules filtered through the bag's membrane and into the water, leaving the larger molecules behind in the bag. After further testing, Harden discovered that the yeast enzyme apparently consisted of two parts: a large-molecular part that could not survive boiling and was almost certainly a protein; and a small-molecular part that could survive boiling and was probably not a protein. (Harden called the nonprotein a coferment, but others soon began calling it a coenzyme.)
Several researchers quickly began studying the newly discovered component's chemical nature and, roughly 20 years later, Hans Euler-Chelpin, a German-Swedish chemist, was able to define its structure. (Harden and Euler-Chelpin shared the 1929 Nobel Prize in chemistry for their work.)
It soon became clear that virtually all coenzymes were composed of vitamins, particularly those in the water-soluble B family. For the most part, they functioned primarily in energy transfers and in the metabolism of fats, carbohydrates, and proteins. During the 1930s Swedish biochemist Axel Theorell (1903-1982) and American biochemist Conrad Arnold Elvehjem (1901-1962) greatly furthered the understanding of vitamins through independently conducted research on oxidation enzymes and pellagra, respectively.
In 1947, a coenzyme particularly important in the metabolic process, Coenzyme A, or CoA, was discovered by Fritz Lipmann, a German-born American biochemist who received the 1953 Nobel Prize in medicine and physiology for the discovery. Feodor Lynen is also remembered for his research on CoA; because he succeeded in isolating acetylcoenzyme A (CoA combined with the two-carbon fragment first theorized by Lipmann), he, along with Konrad Emil Bloch, received the 1964 Nobel Prize for medicine and physiology.
Because most vitamins are inactive when first taken into the body, a two-step process must take place. The vitamin must be activated to its coenzyme form (with vitamins B 1, B 2, and B 6, for instance, this means the addition of a phosphate group.) After that, the coenzyme must combine with its proper enzyme partner. Only then can the catalytic activity, for which both are programmed, be set in motion.
This is the complete article, containing 575 words
(approx. 2 pages at 300 words per page).
