Purification and characterization of tomato polygalacturonase converter

Area of Science:

• Biochemistry
• Plant Science
• Food Science

Background:

• Ripe tomatoes contain two forms of polygalacturonase: PG I and PG II.
• Polygalacturonases are enzymes involved in fruit softening during ripening.

Purpose of the Study:

• To isolate and characterize a heat-stable component from tomato fruit that influences polygalacturonase activity.
• To understand the role of this component in the conversion of PG II to PG I.

Main Methods:

• Purification of the polygalacturonase converter using gel filtration, ion-exchange chromatography, and chromatofocusing.
• Determination of the protein's molecular mass and sensitivity to proteases (papain, pronase).
• Investigation of the converter's stability under alkaline conditions.

Main Results:

• A heat-stable polygalacturonase converter (PG converter) was isolated from ripe tomato fruit.
• The PG converter has a relative molecular mass of 102,000 and is inactivated by papain and pronase, indicating it is a protein.
• The converter facilitates the conversion of PG II to PG I and can be cleaved at alkaline pH (11) to release PG II.
• A similar, lower molecular mass factor was found in tomato foliage.

Conclusions:

• A novel protein, the PG converter, has been identified in tomatoes, mediating the conversion of PG II to PG I.
• This converter plays a significant role in the enzymatic processes of tomato fruit ripening.
• The findings provide insights into the biochemical mechanisms regulating polygalacturonase activity in plants.