Purification and Characterization of Barley Dipeptidyl Peptidase IV1

• Published in: Plant physiology (Bethesda) 2000-02, Vol.122 (2), p.425-432
• Main Authors: Davy, Anne, Thomsen, Karl Kristian, Juliano, Maria A., Alves, Lira C., Svendsen, Ib, Simpson, David J.
• Format: Article
• Language: English
• ISSN: 0032-0889; 1532-2548

Barley ( Hordeum vulgare L.) storage proteins, which have a high content of proline (Pro) and glutamine, are cleaved by cysteine endoproteases to yield peptides with a Pro next to the N-terminal and/or C-terminal amino acid residues. A peptidase cleaving after Xaa-Pro- at the N terminus of peptides was purified from green barley malt. It was identified as a serine-type dipeptidyl peptidase (DPP), based on inhibitor studies, and the nature of the cleavage product. It is a monomeric glycoprotein with an apparent molecular mass of 105 kD (85 kD after deglycosylation), with a pI of 3.55 and a pH optimum at 7.2. Substrate specificity was determined with a series of fluorogenic peptide substrates with the general formula Xaa-Pro-AMC, where Xaa is an unspecified amino acid and AMC is 7-amino-4-methylcoumarin. The best substrates were Xaa = lysine and arginine, while the poorest were Xaa = aspartic acid, phenylalanine, and glutamic acid. The K m values ranged from 0.071 to 8.9 μ m , compared with values of 9 to 130 μ m reported for mammalian DPP IVs. We discuss the possible role of DPP IV in the degradation of small Pro-containing peptides transported from the endosperm to the embryo of the germinating barley grain.