An antioxidant protein in Curcuma comosa Roxb. Rhizomes

Curcuma comosa Roxb. is an indigenous Thai herb which is usually used as a food ingredient but it is also used in traditional folk medicine for the treatment of uterine inflammation. The crude protein extract from the rhizomes of this plant was found to possess free radical scavenging capacity, as detected by the DPPH assay. This antioxidant activity was purified by DEAE anion exchange chromatography to a fraction (called IE-1) that was comprised of a single main protein band of ∼18 kDa (UB-DEAE), as determined by SDS–PAGE resolution with Coomassie blue staining, and had a specific activity of 193.8 U/mg. In-gel trypsin digestion of the SDS–PAGE resolved UB-DEAE band followed by liquid chromatography–tandem mass spectrometry produced three reliably sequenced peptides, which all were found to very likely be fragments of a superoxide dismutase homologue (SOD, EC 1.15.1.1), an antioxidant enzyme that has been found in several plants. In support of this notion, the IE-1 fraction was found to yield positive results with the riboflavin–nitroblue tetrazolium (NBT) assay, a standard test for SOD-like activity. Together, these data then support the existence of an SOD homologue antioxidant protein in the rhizomes of C. comosa as a contributing agent to the total observed antioxidant activity.