Vitamin amino acids. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, vitamin E consists of four tocopherols and four tocotrienols. The thirteen vitamins required by human metabolism are: vitamin A (retinols and carotenoids), vitamin B (thiamine), vitamin B (riboflavin), vitamin B (niacin), vitamin B (pantothenic acid), vitamin B (pyridoxine), vitamin B (biotin), vitamin B (folic acid or folate), vitamin B (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones). Vitamins have diverse biochemical functions. Some forms of vitamin A function as regulators of cell and tissue
Citroën Type B2 apparent to most competitors. Nevertheless, the importance of the Type B10 sometimes tempts commentators who view history only backwards to overlook the Citroën Type B2. For contemporary observers there could be no doubt about the significance of the Citroën Type B2, Europe's second mass-produced car, with 89,841 cars manufactured during a five-year period. The automobile business in France still contained a massively diverse range of companies in what had, till a few years before the outbreak of war, been the world's leading country for automobile production. But in 1925 there was no other manufacturer anywhere in Europe with anything approaching