Napin

Napin is one of the two most abundant seed storage proteins in mustard and rapeseed ("Brassica napus" L., "B. juncea" L. Czern., "B. nigra" L. W.D.J.Koch, "B. rapa" L. and "Sinapis alba" L.). They are water soluble low-molecular weight basic proteins classified as 2S or 1.7S proteins, representing 20–40% of total seed protein, and having a molecular weight in the range of 12–17 kDa. Their isoelectric point varies based on the method of extraction and the specific characteristics of the isoforms that exist. They are composed of two polypeptide chains, a 4.5 kDa small subunit and a large 10 kDa subunit, stabilized primarily by disulphide bonds. Their secondary structure shows a high α-helical content.