Rice bifunctional alpha-amylase/subtilisin inhibitor: characterization, localization, and changes in developing and...

Area of Science:

• Plant biochemistry
• Enzyme inhibition studies
• Proteomics

Background:

• Alpha-amylase and subtilisin are enzymes with diverse biological roles.
• Protease and amylase inhibitors are crucial in plant defense and seed physiology.
• Rice (Oryza sativa L.) is a staple food crop, and understanding its endogenous proteins is important.

Purpose of the Study:

• To purify and characterize a bifunctional inhibitor from rice bran.
• To investigate the inhibitory activity of the purified protein against various proteases and amylases.
• To determine the localization and synthesis timing of the inhibitor in rice grains.

Main Methods:

• Protein purification using electrophoretic homogeneity.
• Enzyme inhibition assays with various proteases (subtilisin, trypsin, chymotrypsin) and amylases (rice, barley, mammalian).
• SDS-PAGE for molecular mass determination.
• Isoelectric focusing for isoelectric point determination.
• Western blotting for synthesis and localization studies.

Main Results:

• A bifunctional alpha-amylase/subtilisin inhibitor (RASI) was purified from rice bran.
• RASI has a molecular mass of 21 kDa and an isoelectric point of 9.05.
• RASI strongly inhibited subtilisin Carlsberg and weakly inhibited rice alpha-amylase, with greater inhibition at higher pH.
• RASI showed differential inhibition of alpha-amylase from different species (rice > barley).
• RASI did not inhibit trypsin, chymotrypsin, cucumisin, or mammalian alpha-amylase.
• RASI is located in the outer part of the rice grain (aleurone cells) and synthesized during seed development.

Conclusions:

• Rice contains a unique bifunctional inhibitor (RASI) targeting both alpha-amylase and subtilisin.
• RASI exhibits specific inhibitory activity, with variations based on enzyme source and pH.
• The inhibitor's localization and synthesis pattern suggest a role in rice seed physiology and potentially defense.