Three multiple forms of polygalacturonase (PG) in ripe and two in unripe banana (Musa
acuminata) fruits were separated by DEAE-cellulose and further purified using Sephadex
G-150 chromatography. The multiple forms can be differentiated from each other on
the basis of their properties. PG1 and PG3 were identified as endo-PG and PG2 as exo-PG
on the basis of decrease in viscosity, increase in reducing sugar and the reaction
product. PG2 and PG3 increased with the ripening of fruits. PG1, PG2 and PG3 exhibited
optimum activity at pH 3.3, 3.7 and 4.3, respectively. Complete loss of PG2 and PG1
activities occurred at 60 and 70 degrees, but PG3 retained 60 and 50% activity respectively.
The three forms showed a different response towards divalent metal ions. Ca2+ activated
PG1 activity only. Teepol 0.1%, inhibited PG1 activity by 25%, but PG2 and PG3 activities
were completely inhibited. CTAB, 0.1%, had no effect on PG1 and PG2 activities, but
inhibited PG3 activity by 40%. 2-ME stimulated PG2 and PG3 activities but had no effect
on PG1 activity. Gel filtration through Sephacryl indicated M(r) of 23,200, 58,000
and 130,000, respectively, for PG1, PG2 and PG3. The substrate saturation curve for
PG1 and PG2 were Michaelian, while PG3 showed biphasic curve. The Km values of PG1
and PG2 were 0.22% and 0.14%, respectively.