Extraction and Assay of Tomato Polygalacturonases

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Abstract
The conditions for extracting and assaying tomato (Lycopersicon esculentum Mill.) polygalacturonases (PG I and PG II) have been re-examined. The enzymes were not extracted by water at pH 3, which allowed washing of the cell wall fraction to remove the soluble components that interfere in the PG assay. The extractability of PG in water increased as the pH was lowered or raised from 3, with optima near pH 1.8 and 6.5. Only PG II was extracted by water at pH 1.8, whereas both isoenzymes were extracted at pH 6.5. The extractabilities of the PGs were increased by NaCl, but the amount of total activity extracted by 1.2 m NaCl was independent of pH between 2 and 9. Extracts in 1.2 m NaCl of pH 3 washed cell walls from ripe tomatoes could be assayed without concentration or dialysis. Higher PG activity was recovered when extracts were concentrated by ultrafiltration than by precipitation with (NH4)2SO4. The results indicate that the isoenzyme composition and recovery of PG from tomatoes were dependent on extraction and concentration procedures.

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