Stevia rebaudiana, a Versatile Food Ingredient: The Chemical Composition and Medicinal Properties

Table 2

Some of the free radicals’ potential harm to biomolecules in the body.

Species	Source	Reaction(s) with biomolecules
O2·^-	Enzymatic process, autoxidation reaction, and nonenzymatic electron transfer reactions	It can act as reducing agent of iron complexes such as cytochrome-c or oxidizing agent to oxidize ascorbic acid and α-tocopherol
HO2·	Protonation of O2·	Initiates fatty acid peroxidation
HO·	H2O2 generates HO· Through the metalcatalyzed Fenton reaction	HO· reacts with both organic and inorganic molecules including DNA, proteins, lipids, and carbohydrates
NO·	Action of nitric oxide synthase using arginine as a substrate and NADPH as an electron source	NO· is an intracellular second messenger stimulates guanylate cyclase and protein kinases and helps in smooth muscle relaxation in blood vessels
NO2·	Protonation of ONOO· Or homolytic fragmentation of ONOOCO2·	This radical acts on the antioxidative mechanism decreasing ascorbate and α-tocopherol in plasma
ONOO·	Reaction of O2· With NO.	ONOO. is a strong oxidizing and nitrating species of methionine and tyrosine residues in proteins and oxidizes DNA to form nitroguanine
CO3·^-	The intermediate of reaction superoxide dismutase (SOD)-Cu2^+-OH· react with bicarbonate to generates CO3·^-	Oxidizes biomolecules such as proteins and nucleic acids
ONOOCO2^-	The peroxynytrite-CO2 adduct is obtained by reaction of ONOO^- with CO2	This anion promotes nitration of tyrosine fragments of the oxyhemoglobin via free radicals