GERMINATED OATS PROTEINASES THAT HYDROLYZE AVENINS

Authors: MIKOLA, M - UNIVERSITY OF HELSINKI; BRINCK, O - UNIVERSITY OF HELSINKI; Jones, Berne

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 1/20/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: When seeds start to grow, they need to break their stored proteins down in order to obtain nutrients for the growing plantlet. It is important to understand how this protein breakdown occurs, because malted (germinated) oats are used in foods and, to get the best nutritive values and taste characteristics, we need to know how to alter the protein breakdown patterns. One group of proteins that are stored in oat seeds for use by the growing plantlet is called avenin. In this study, we started oat seeds growing and checked to see when they made enzymes that degraded the three different avenin forms that occur in the seed. The three avenin forms ("-, $1- and $2-) were hydrolyzed by enzymes that formed on the third, eighth and sixth days of germination, respectively. There are 4 different types of common protein-degrading enzymes, and we determined that all of the oat ones belonged to the cysteine class proteases. We had found that a second type of oat storage proteins, called globulins, was broken down by enzymes that had different characteristics, so it seems likely the two protein types are degraded by different enzymes. The information gained in this study will allow researchers and industry personnel to produce different food types from oats by altering their processing methods or oat varietal characteristics to preferentially degrade the different kinds of storage proteins that are present in ungerminated oat grains.

Technical Abstract: In resting seeds, storage proteins are generally stockpiled in an insoluble form and must be solubilized during germination so that they can be used by the growing plantlet. Little is known about the proteolytic system of germinating oats, so this study was carried out to characterize the proteinases that hydrolyze the oat storage proteins that are called avenins. The avenins were hydrolyzed by proteinases extracted from germinated seeds and the hydrolysis products were analyzed by SDS-PAGE. The avenin preparation contained "-avenins and $1- and $2-avenins. The "-avenins were hydrolyzed by enzymes from 3-day germinated seeds, while the $-1 and $-2 were only degraded by extracts prepared from 8-day and 6-day germinated seeds, respectively. The addition of class-specific protease inhibitors to the reactions showed that, at pH 3.8, the active proteases were all cysteine-class enzymes. Previous studies had shown that oat globulins were degraded by proteases that had somewhat different characteristics, so it seems likely that these two storage protein classes are hydrolyzed by different enzymes. This work indicates that the different avenin forms are also hydrolyzed by different proteases. The pH of germinating oat seed endosperms is about 6.2, while the proteinases were all most active at pH 3.8, indicating that it is likely that some pH compartmentalization occurs within the germinating seed.