Glutinous rice (Oryza sativa L.) protein extract with potent α-amylase inhibitory activity

Abstract

This research screened for α-amylase inhibitory activity of twenties-five varieties Thai indigenous rice seeds. Based on specific inhibition, crude protein of var. Gai Ngaw (Gs. No. 13719) was selected for purification. The unbound proteins of the Q-Sepharose column named partially purified rice α-amylase inhibitor (RAI) revealed MW of approximately 14.4 kDa. The RAI was stable at pH 4 to 7 and heat stable up to 80 °C. The RAI had IC₅₀ of 15.92 ± 1.08 µg/ml. The double reciprocal plot implied a mixed-type inhibitor. The Dixon and Cornish-Bowden plots were used to estimate Ki and αKi. This suggested Thai indigenous rice seeds could potentially be developed as a food supplement for blood sugar and weight controls.

Keywords: Blood sugar lowering; Indigenous rice; Mixed-type inhibition; Weight control; α-amylase inhibitor protein.

Fig. 1

Q-Sepharose column profile of the 40% saturated (NH₄)₂SO₄ precipitated protein of var. Gai Ngaw (Gs. No.13719). The elution was performed by a linear gradient of 0–0.5 M NaCl in 20 mM Tris–HCl buffer, pH 8.6. (a); and 15% SDS-PAGE of purified RAI; Lane M: molecular weight markers; lane 1: crude protein; lane 2: 65 °C heat stable protein; lane 3: 40% sat. (NH₄)₂SO₄ precipitated protein; lane 4: UBQ; lane 5: BQ1; lane 6: BQ2; lane 7: BQ3. Loaded protein 0.9 µg (b) and Purification table of Thai rice seed α-amylase inhibitor (c)

Fig. 2

Double reciprocal plot of porcine pancreas α-amylase with various concentrations of starch by fixing the concentration of RAI (a); Secondary plot between the concentration of inhibitor and slope (b); Secondary plot between the concentration of inhibitor and vertical axis intercept (c); Dixon plot of porcine pancreas α-amylase in the presence of different concentrations of RAI by fixing the concentration of substrate (d) and Cornish-Bowden plot of porcine pancreas α-amylase in the presence of different concentrations of RAI by fixing the concentration of substrate (e)

Fig. 2

Double reciprocal plot of porcine pancreas α-amylase with various concentrations of starch by fixing the concentration of RAI (a); Secondary plot between the concentration of inhibitor and slope (b); Secondary plot between the concentration of inhibitor and vertical axis intercept (c); Dixon plot of porcine pancreas α-amylase in the presence of different concentrations of RAI by fixing the concentration of substrate (d) and Cornish-Bowden plot of porcine pancreas α-amylase in the presence of different concentrations of RAI by fixing the concentration of substrate (e)