Ascorbate as a free radical scavenger and antioxidant has been known for decades. Recent observations highlight the role of ascorbate in the regulation of metabolism; this function is predominantly fulfilled by its redox properties. The importance of ascorbate is underlined by the fact that the molecule is synthesized by all eukaryotes, with the exception of primates and some other animals, which have lost gulonolactone oxidase activity; in these species, however, ascorbate is an indispensable vitamin.

The aim of this chapter is to show the role of ascorbate in the integration of cellular metabolism from the regulation of enzymatic activities to the regulation of gene expression as a transcriptional regulator or an epigenetic factor. Furthermore, the subcellular distribution of ascorbate influenced by the transporters of endomembranes and mitochondrial membranes is also emphasized. Recent observations show that not only the general shortage of cellular ascorbate but also its local deficit due to overconsumption and/or the decreased capacity of transporters can establish a pathologic condition.