Vitamin C (ascorbic acid) is an essential reducing agent for the biosynthesis of collagen, an important connective tissue protein. (In fact, collagen is the most abundant protein in the body). Vitamin C maintains the iron atom of prolyl hydroxylate in the ferrous state. Prolyl hydroxylase carries out the hydroxylation of collagen, which gives the fibers their strength. Collagen synthesized absent Vitamin C is insufficiently hydroxylated. Scurvy, vitamin C deficiency, for example, is caused when there is insufficient vitamin C to carry out proper collagen synthesis.