Purification and characterization of polygalacturonase from banana fruit

Polygalacturonase isoenzyme 3 (PG-3) was purified to homogeneity with a spe cific activity of 0.7 mu katal mg(-1) protein from banana fruit pulp. The p urified enzyme was a glycoprotein with ca. 8% carbohydrate. The molecular w eight of the native enzyme was found to be 90 +/- 10 kDa with a subunit mol ecular weight of 29 +/- 2 kDa. The enzyme exhibited optimum activity at pH 4.3 and temperature 40 degrees C with activation energy 35.4 kJ mol(-1). A unique property of the enzyme was the requirement of SH groups for the enzy me activity. The enzyme was inhibited by p-CMB and activated by 2-ME and DT T. The inhibition of p-CMB could be reversed by DTT. The enzyme contained e ight free -SH groups. The K-m of the enzyme was 0.15% for polygalacturonic acid. (C) 2000 Elsevier Science Ltd. All rights reserved.