A novel α-glucosidase inhibitor protein from the rhizomes of Zingiber ottensii valeton.

The objective of this study was to investigate a new protein with α-glucosidase inhibitory activity from the rhizomes of Zingiber ottensii. With a simple salting-out technique followed by single-step anion-exchange purification, the protein was successfully purified from the rhizomes. This protein was found to have three likely sub-unit types, 32.5, 15.2, and 13.8 kDa, as revealed by native and reducing SDS-PAGE analysis. Determination of the kinetics of the inhibition of α-glucosidase from Saccharomyces cerevisiae by standard enzymatic methods indicated the maximum percent inhibition; IC(50) and K ( i ) of this protein were 77.5%, 30.15 μg/ml, and 140 μmol, while the K ( m ) and V ( max ) were 2.35 μmol and 0.11 mM/min, respectively. The inhibitory action was pH-independent within the pH range 2-10, but was potentially affected by buffer salts, and was relatively temperature-stable between 4-35 °C, with a maximum activity at 65 °C. The amino acid sequence of an internal fragment of this purified Z. ottensii rhizomal protein had a similarity to the sequence from the plant cysteine proteinase family. Although this α-glucosidase inhibitory protein was purified from Z. ottensii rhizomes and preliminarily characterized, further studies are needed prior to firm applications being envisaged.