Vitamin C as cells rapidly reduce dehydroascorbic acid to ascorbate. SVCTs appear to be the predominant system for vitamin C transport in the body, the notable exception being red blood cells, which lose SVCT proteins during maturation. In both vitamin C synthesizers (example: rat) and non-synthesizers (example: human) cells with few exceptions maintain ascorbic acid concentrations much higher than the approximately 50 micromoles/liter (µmol/L) found in plasma. For example, the ascorbic acid content of pituitary and adrenal glands can exceed 2,000 µmol/L, and muscle is at 200-300 µmol/L. The known coenzymatic functions of ascorbic acid do not require such high concentrations, so
Vitamin C and also regenerator of other antioxidants. Plants use multiple pathways to synthesize vitamin C. The major pathway starts with glucose, fructose or mannose (all simple sugars) and proceeds to L-galactose, L-galactonolactone and ascorbic acid. There is feedback regulation in place, in that the presence of ascorbic acid inhibits enzymes in the synthesis pathway. This process follows a diurnal rhythm, so that enzyme expression peaks in the morning to support biosynthesis later on when mid-day sunlight intensity demands high ascorbic acid concentrations. Minor pathways may be specific to certain parts of plants; these can be either identical to the vertebrate pathway